MailKit

• SECURITY: Fixed protocol streams to reset internal buffers after upgrading to SSL/TLS.
• Dispose of the RandomNumberGenerator used in RC4.GenerateKey(). (issue #1989])
• Fixed calculation for number of needed bytes in SOCKS5 connect response. (issue #1993)

• SECURITY: Bumped MimeKit to 4.15.1 for a security fix that prevents mailbox addresses from being allowed to contain CRLF sequences which can be used to inject SMTP commands in the SmtpClient when it sends MAIL FROM or RCPT TO commands.

• Default the SmtpClient/Pop3Client/ImapClient.SslProtocols to the ServicePointManager.SecurityProtocol value in .NET Framework (net4x). (issue #1952)
• Added support for.NET 10.
• Marked IMailService.SslCipherAlgorithm, SslCipherStrength, SslHashAlgorithm, SslHashStrength, SslKeyExchangeAlgorithm, and SslKeyExchangeStrength as Obsolete in .NET 10 in favor of the IMailService.SslCipherSuite property (.NET 10 only).
• Bumped MimeKit dependency to 4.15.0.

• Re-added NTLM to the list of mechanisms to try by default. (issue #1953)
• Fixed IMAP to treat '+' as a normal Atom token. (issue #1956)
• Added fallback logic for imap.strato.de if LIST doesn't return the INBOX. (issue #1957)

• Updated MailService::GetSslClientAuthenticationOptions to be protected virtual. (issue #1931)
• Fixed initialization of SaslMechanism to lazily check if GSSAPI and/or NTLM are supported (natively) to avoid undesirable error messages appearing in dotnet logs on Linux systems. (issue #1924)
• Bumped MimeKit dependency to 4.14.0.

• Fixed tokenization of IMAP atom tokens that start with '+'. (issue #1914)
• Fixed the Imap/Pop3/Smtp clients to no longer fallback to using the ServicePointManager.ServerCertificateValidationCallback method on .NET Core. (issue #1925)
• Bumped MimeKit dependency to 4.13.0.

• Fixed authentication bugs introduced into 4.12.0 related to adding GSSAPI and native NTLM auth support which causes problems on Linux/Mac. (issue #1910 and #1911)
• Reverted System.Threading.Tasks.Extensions dependency back to 4.6.2.
• Reverted System.Formats.Asn1 dependency back to 8.0.1.

• Added support for native NTLM auth (using .NET Core's NegotiateAuthentication API). This new class is called SaslMechanismNtlmNative and is the default NTLM mechanism used by MailKit clients on net8.0+.
• Added support for the GSSAPI SASL mechanism for net8.0+. (issue #1249)
• Fixed MailFolder.FirstUnread to be initialized to -1 to indicate unknown. (issue #1898)
• Added support for non-compliant keywords that begin with ''. (issue #1906)
• Added SearchQuery.HasKeywords/NotKeywords() overloads that take params instead of IEnumerable<string>.
• Bumped System.Threading.Tasks.Extensions from 4.6.2 to 4.6.3.
• Bumped System.Formats.Asn1 from 8.0.1 to 8.0.2.
• Bumped MimeKit dependency to 4.12.0.

• Default MailService.SslProtocols to SslProtocols.None which is what the dotnet SslStream team recommends. (As weird as it may seem, SslProtocols.None does not mean "don't support any SSL protocols", it means don't override the default system settings.)
• Bumped MimeKit dependency to 4.11.0.

• Work around a QQMail/Yandex IMAP BODYSTRUCTURE response for empty multipart. (issue #1861)
• Added exception documentation for methods in IMailFolder. (issue #1868)
• Added IMailFolder.CanOpen property that checks IMailFolder.Attributes for NoSelect and NonExistent flags.
• Bumped MimeKit dependency to 4.10.0.

• Added an IMAP work-around for mail.ru which sometimes sends integer tokens as decimals in its responses. (issue #1838)
• Added a workaround for GMail IMAP BODY responses that include multipart expressions without any children (e.g. ("ALTERNATIVE")). (issue #1841)
• Fixed default system proxy to handle null credentials and check if the targetUri is bypassed. (issue #1852)
• Dropped support for net6.0 (Microsoft support ended Nov 12, 2024).
• Bumped System.Threading.Tasks.Extensions dependency to 4.6.0.
• Bumped MimeKit dependency to 4.9.0.

• Added a UniqueIdRange.SortOrder property.
• Updated the protocol log help link for ProtocolExceptions. (issue #1800)
• Fix SmtpClient.Dispose() when telemetry is configured. (issue #1816)
• Added ProxyClient.SystemProxy as a convenience property that wraps the default system proxy (aka HttpClient.DefaultProxy) on net6.0+.

• Fixed ImapClient and Pop3Client.Connect/Async() when OTEL is enabled. (issue #1765)
• Bumped MimeKit dependency to 4.7.1 to fix a denial of service security issue in the System.Formats.Asn1 dependency.

• Added Activity/Metrics for Imap/Pop3/SmtpClient. (issue #1499)
• Bumped MimeKit dependency to 4.7.0.

• Swallow SMTP RSET exceptions. These obscure other Send/SendAsync exceptions. Fixes a regression introduced in 4.4.0. (issue #1748)
• Fixed ImapUtils.FormatInternalDate() to properly handle negative timezone offsets with non-zero minutes. (issue #1743)
• Bumped MimeKit dependency to 4.6.0.

• Added a new SmtpClient.RequireTLS property to fix sending mail via Strato.de. (issue #1737)
• Fixed SmtpClient to track the most recent response from the SMTP server in order to include it in SmtpProtocolExceptions caused by unexpected server disconnects to provide more context. (issue #1744)
• Bumped MimeKit dependency to 4.5.0.

• Added net8.0 targets
• Split more sync/async logic to reduce allocations made by async state machines when calling the synchronous public APIs instead of the async APIs. (issue #1335)
• Fixed logic for formatting IMAP FETCH HEADER.FIELDS.NOT corner case that was exposed by newly added unit tests.
• Fixed SmtpClient to disconnect during Authenticate/Async on socket errors.
• Fixed SmtpClient's re-EHLO logic to disconnect on errors.
• Added workaround for Zoho IMAP servers returning MODSEQ -1. (issue #1686)
• Added workaround for some IMAP servers that use () instead of NIL for an unset Content-Location header in the BODYSTRUCTURE response. (issue #1700)
• Fixed an issue in the Socket.ConnectAsync logic that could result in unhandled exceptions on the async thread if the ConnectAsync was cancelled. (issue #1703)
• Added work-around for Yandex IMAP GetBodyPart() response not including content. (issue #1708)
• Bumped MimeKit dependency to 4.4.0.

• Fixed an ArgumentOutOfRangeException error in Fetch(int min, int max, ...) where min and max were greater than folder.Count. (issue #1640)
• Fixed parsing of IMAP FETCH (message/stream) responses with unsolicited FLAGS.
• Fixed support for the IMAP FILTERS extension. Previously this extension was not properly detected.
• When parsing IMAP CAPABILITIES, treat lone '+' tokens as atoms. (issue #1654)
• Bumped MimeKit dependency to 4.3.0.

• Fixed a bug where the HttpProxyClient and HttpsProxyClient could end up reading the mail server greeting, causing a connection failure for the ImapClient/Pop3Client/SmtpClient. (issue #1603)
• Parse IMAP quota values as ulongs instead of uints for GMail compatibility. (issue #1602)
• Added support for decoding SMTP DATA to the SmtpDataFilter. (issue #1607)
• Added a Pop3Client.Size property. (issue #1623)
• Refactored more ImapClient commands to split sync/async implementations in order to improve performance and reduce GC pressure. (issue #1335)
• Added new IMailFolder.GetStream() methods that just take a uid/index and a BodyPart.
• Added IMailFolder.GetStream/Async() methods that just take a uid or index.
• Improved initial List<IMessageSummary> capacity estimation for Fetch (IList<UniqueId>, ...).
• Fixed ByteArrayBuilder.TrimNewLine() to check array bounds properly. (issue #1634)
• Bumped MimeKit dependency to 4.2.0.

• Fixed queueing logic for pipelining SMTP and POP3 commands. (issue #1568)
• Improve SslHandshakeException diagnostic messages. (issue #1554)
• Bumped System.Formats.Asn1 dependency to 7.0.0.
• Bumped MimeKit dependency to 4.1.0.

• Marked the AccessRight and UniqueId structs as readonly.
• Fixed POP3 client logic to calculate the needed bytes before converting commands into into the output buffer.
• Ported to MimeKit v4.0 and BouncyCastle v2.1.1.

• Decrement ImapFolder.Count when ImapClient receives an untagged EXPUNGE notification and emit a CountChanged event. (issue #1509)
• Avoid using the NAMESPACE command for Exchange 2003. (issue #1512)
• Added support for rfc8970 (IMAP4 Extension: Message Preview Generation).

• Fixed bitmasking logic in SmtpClient.cs for deciding whether to use the BDAT command.
• Fixed HttpProxyClient to call GetConnectCommand() before connecting a socket to prevent memory leaks when connecting fails.
• Improved the IMAP BODYSTRUCTURE parser to better handle broken responses.
• Fixed bug in Envelope.Parse/TryParse when given (NIL NIL "" "localhost") (issue #1471)
• Fixed SMTP client logic to calculate the needed bytes before converting commands into into the output buffer. (issue #1498)
• Fixed SmtpClient to replace _'s with -'s in the default LocalDomain string (used in HELO/EHLO commands). (issue #1501)

• Fixed potential memory leaks in Pop3Client.
• Reverted SMTP pipelining of the DATA command. (issue #1459)
• Fixed ImapFolder.Rename() to disallow renaming a folder to be a child of itself.
• Fixed SmtpStream.ReadResponse/Async() to handle buffers that do not contain a complete line. (issue #1467)

• Fixed fetching of MessageSummaryItems.PreviewText if the octet count of the message body is 0. (issue #1430)
• Modified ImapFolder.Search(SearchOptions.None, query) work the same as ImapFolder.Search(query). (issue #1437)
• Improved performance of SmtpClient by reducing memory allocations and pipelining the DATA command when the PIPELINING extension is available.
• Refactored sync and async SmtpClient APIs such that the synchronous APIs no longer call methods marked with async in order to reduce AsyncMethodBuilder state machines/allocations.
• Modified SmtpClient to only send the ORCPT argument to RCPT TO if NOTIFY is specified.
• Improved performance of Pop3Client by reducing memory allocations.
• Refactored sync and async Pop3Client APIs such that the synchronous APIs no longer call methods marked with async in order to reduce AsyncMethodBuilder state machines/allocations.
• Improved IMAP's BODY/BODYSTRUCTURE parser to be able to scan ahead multiple tokens in order to better handle syntactically incorrect responses in a more graceful way. (issue #1446)
• Improved IMAP's ENVELOPE parser to handle ("Microsoft Exchange Server" NIL NIL ".MISSING-HOST-NAME.") in a more graceful way. (issue #1451)

• Reverted the socket connection change to allow Socket.Connect() to do DNS lookups for us. Turns out, Socket.Connect() doesn't iterate over all returned IP addresses until it finds an IP address that it can successfully connect to for a given hostname which is what we need to do.

• Fixed a bug that caused ImapFolder.Fetch/FetchAsync to throw TaskCanceledException instead of allowing the correct exception to bubble up. (issue #1415)
• Simplified socket connection logic to allow Socket.Connect() to do DNS lookups for us.
• Updated common mail server SSL certificates.
• Dropped net5.0 support.

• Added work-around for IMAP BODYSTRUCTURE responses that have a NIL multipart body. (issue #1393)
• Considerably reduced memory overhead from compiler-generated async/await Tasks allocations in the IMAP implementation (mostly focused on FETCH commands/responses). (issue #1335)
• Optimized FETCH response processing for the common case where FETCH responses are returned in sorted order.
• Fixed the IMAP Literal string reader to use UTF-8 with fallback to iso-8859-1 (previously just used iso-8859-1).
• Modified the IMAP ENVELOPE parser to combine ENVELOPE mailbox tokens if there are more than 4. (issue #1369)
• Prevent TypeLoadExceptions in the SmtpClient static .ctor by catching NotSupportedExceptions thrown by IPGlobalProperties.GetIPGlobalProperties() on platforms like WASM. (issue #1381)
• Updated Google, GMX, and Yahoo! Mail SSL certificates.
• Dropped support for net452 and net461.
• Added support for net462.

• Do not use ApplicationProtocols with SSL. (issue #1352)
• Updated GMail, Yahoo, and Outlook.com certificates.
• Lazy-initialize MessageSummary.Keywords. This reduces memory usage when the client isn't requesting Flags/Keywords.
• Hard-cache some IMAP FETCH-related tokens in order to relieve GC pressure for commands like FETCH where there can be a LOT of responses containing the same tokens over and over again.
• Converted some IMAP async Task methods to use ValueTask to reduce GC pressure.
• Reduced string allocations in the IMAP logic by avoiding use of ToUpperInvariant().
• Added non-async implementations for ImapStream APIs to be used by the synchronous public APIs to avoid some async overhead.
• Reduce MemoryStream (and thus byte[]) allocations by using a new ByteArrayBuilder.
• Rewrote the IMAP CAPABILITY parser to avoid allocating strings.
• Fixed some cases where IMAP NIL tokens were not compared case insensitively.
• Always include the VERSION block in NTLM messages. (issue #1340)
• Target .NET Framework v4.6.1 instead of v4.6 to match the changes in MimeKit.
• Capture the Socket timeout value in Read/WriteAsync() to have it in case of exceptions. (issue #1327)

• Reduced string allocations in Pop3Engine's capability parser.
• Updated GMail and Outlook.com SSL certificates.
• Modified SmtpClient to try and use the system hostname in EHLO/HELO commands. (issue #1314)

• Fixed NTLM to always prefer the supplied domain over the TargetName or TargetInfo.DomainName. (issue #582)
• Updated GMail and Outlook.com SSL certificate info.
• Added a new SslCipherSuite property to each client that allows developers to get information about the SSL/TLS cipher suite that was negotiated with the server. (pull #1312)
• Reduced string allocations in SmtpClient's EHLO capability parsing logic.
• Default ProtocolLogger.RedactSecrets to true for added added security.
• Added work-around for parsing malformed GMail ENVELOPE responses that reverse the name and address components of the Sender address. (pull #1319)
• Added net6.0 to the list of TargetFrameworks.

• Removed APIs marked as [Obsolete] in 2.x.
• Simplify Fetch()/FetchAsync() APIs by using a new IFetchRequest parameter instead. Made previous APIs into extension methods to aid in porting from 2.x.
• Replaced Add/Remove/SetFlags() APIs with Store()/StoreAsync() and simplified the APIs by using a new IStoreFlagsRequest parameter. Made previous APIs into extension methods to aid in porting from 2.x.
• Replaced Add/Remove/SetLabels() APIs with Store()/StoreAsync() and simplified the APIs by using a new IStoreLabelsRequest parameter. Made previous APIs into extension methods to aid in porting from 2.x.
• Simplify Append()/AppendAsync() APIs by using a new IAppendRequest parameter instead. Made previous APIs into extension methods to aid in porting from 2.x.
• Simplify Replace()/ReplaceAsync() APIs by using a new IReplaceRequest parameter instead. Made previous APIs into extension methods to aid in porting from 2.x.
• Updated SmtpClient.Send()/SendAsync() methods to return a string. (issue #1161)
• Added support for the SCRAM-SHA*-PLUS SASL mechanisms. (issue #950)
• Added authzid support for SCRAM SASL mechanisms.
• Added support for the ANONYMOUS SASL mechanism.
• Added support for an HttpsProxyClient. (issue #1251)
• Added AcceptedKeywords and PermanentKeywords to IMailFolder. (issue #1256)
• Rewrote NTLM support based on official specs. Now supports channel-binding and using the default system credentials.
• Modified ImapFolder.Fetch(int, int, ...) to shortcut if ImapFolder.Count == 0.
• Updated SmtpClient to append an ORCPT arg to RCPT TO commands and to hex-encode the ENVID parameter value.
• Improved/simplified logic for ranking SASL authentication mechanisms for each client.
• Added SaslMechanism.ChallengeAsync() to facilitate future SASL mechanisms that may need to make network requests such as Kerberos/GSSAPI and perhaps even future/custom OAuth2 implementations.
• Always set SearchResults.Count/Min/Max properties if we can.
• Throw TimeoutException is case of a network time out. (issue #1269)
• Fixed parsing of IMAP flag lists to handle lowercase flag names. (issue #1277)
• Use OrdinalIgnoreCase when comparing "EARLIER" atom token.
• Avoid unnecessary string copies. (issue #1292)
• Drop support for .NET 4.5 and replace it with .NET 4.5.2
• Simplified event emissions based on EXISTS and EXPUNGED notifications. A CountChanged event is now always emitted when the server sends an EXISTS notification. (issue #1288)

• Use DebugType=full for .NET Framework v4.x. (issue #1239)
• Updated GMail SSL certificate serial numbers and fingerprints.
• Small NTLM code improvements.

• Added support for logging timestamps in the ProtocolLogger (see the LogTimestamps and TimestampFormat properties on ProtocolLogger).
• Added support for automatically redacting user credentials in protocol logs. To enable this, set the ProtocolLogger.RedactSecrets property to true. (issue #1174)
• Added the GetMessageSizeAsync() method to the IMailSpool interface. (issue #1233)
• Added a work-around to the IMAP INTERNALDATE parser to handle invalid dates such as "00-Jan-0000 00:00:00 +0000" which appears in Domino IMAP server responses, likely when the INTERNALDATE value is uninitialized in the database. (issue #1236)
• Make sure to dispose X509Certificates in .NET >= 4.6.
• Re-added NTLM as one of the default supported SASL mechanisms.
• Updated GMail SSL certificate serial numbers and fingerprints.

• Added new properties to all clients to get SSL cipher/hash/protocol/key-exchange info. (issue #1175)
• Added support for GMail's WEBALERT resp-code. (issue #1214)
• Updated GMail SSL certificate serial numbers and fingerprints.

• Fixed the .NET 5.0 build to include .NET 5.0-specific features. Previous releases incorrectly used #if NET50 instead of #if NET5_0. (issue #1140)
• Added support for NETStandard 2.1. (issue #1181)
• .NETStandard 2.1 and .NET 5.0 versions of MailKit now use the newer SslStream.AuthenticateAsClientAsync() methods that take SslClientAuthenticationOptions and CancellationToken arguments. In theory, this should make upgrading a TCP/IP connection to SSL/TLS cancellable. Older .NET frameworks remain uncancellable for this operation.
• Fixed a NullReferenceException bug in the NTLM SASL mechanism logic.
• Updated hard-coded SSL certificate serial numbers and fingerprints for common mail servers.

• Added work-around for IMAP servers that do not correctly handle the ESEARCH RETURN () syntax the same as RETURN (ALL). (issue #1177)

• Handle BAD responses to the NAMESPACE command for Exchange. (issue #1135)
• Added support for configuring SSL/TLS cipher algorithms (only available in the .NET 5.0 API). (issue #1140)
• Updated GMail and Yahoo! Mail SSL certificate info.
• Protect against NREs in NTLM authentication of no OSVersion is set. (issue #1148)
• Added work-around for hMailServer bug that doesn't accept seq-ranges in descending order. (issue #1150)
• Properly escape IPv6 addresses for Uri in order to allow Connect/Async methods to work with IPv6 addresses. (issue #1165)
• Added IsEncrypted and IsSigned properties to IMailService. (issue #1175)

• A few NTLM improvements that I hope are correct.

• Don't enable support for TLS v1.1 by default anymore. (issue #1077)
• Added support for the SCRAM-SHA-512 SASL mechanism. (issue #1097)
• Added support for the OAUTHBEARER SASL mechanism.
• Updated SSL certificate info for the common mail servers (GMail, outlook.com, Yahoo! Mail, etc).
• Improved the SslHandshakeException error message to report common mistakes like trying to initiate an SSL connection on a non-SSL port.
• Improved IMAP's "Unexpected token" exception messages a bit
• Updated code to use ArrayPools from System.Buffers.

• Refactored Connect/ConnectAsync() logic to set timeouts before calling SslStream.AuthenticateAsClient() when connecting to an SSL-wrapped service. (issue #1059)
• Hardcode the value of SslProtocols.Tls13 for frameworks that do not support it and add it to the client's default SslProtocols. This adds TLS v1.3 support, by default, for apps using .NETStandard2.0 where the app project is built against a version of .NETCore that supports TLS v1.3. (issue #1058)
• Initialize IMAP SearchResults with the UIDVALIDITY value. (issue #1060)
• Make sure the ImapStream is not null (can be null if user calls Disconnect() causing IDLE to abort). (issue #1025)
• Case-insensitively match IMAP folder attribute flags (e.g. \HasNoChildren and \NoSelect).
• Added support for the IMAP SAVEDATE extension.
• Added support for detecting SMTP's REQUIRETLS extension.

• Make sure to use the InvariantCulture when converting port values to a string. (issue #1040)
• Fixed other instances of string formatting for integer values to always use CultureInfo.InvariantCulture.
• Added a work-around for broken IMAP servers that allow NIL message flags. (issue #1042)

• Added a MessageSummary.Folder property and MessageThread.Message property to allow developers to thread messages from multiple IMAP folders and be able to figure out which folder each message belongs to.
• Added a work-around for IMAP servers that send a UIDNEXT response with a value of '0'. (issue #1010)
• Added an IMailFolder.Supports(FolderFeature) method so that developers can check whether a feature is supported by the folder without needing a reference to the corresponding ImapClient object in order to check the Capabilities.
• Fixed the HTTP proxy client to accept "200 OK" with an empty body as a successful connection. (issue #1015)
• Fixed the SOCKS5 proxy client to correctly send an authentication request. (issue #1019)
• Added support for customizable ProtocolLogger client/server prefixes. (issue #1024)
• Fixed an NRE in SslHandshakeException.Create() when running on Mono/Linux.
• Modified the SmtpClient to take advantage of the SMTPUTF8 extension for the MAIL FROM and RCPT TO commands even if a options.International is not explicitly set to true if any of the mailbox addresses are international addresses. (issue #1026)
• Added support for a new Important SpecialFolder (rfc8457).
• Added support for the IMAP REPLACE extension (rfc8508).
• NuGet packages now include the portable pdb's.

• Properly handle connection drops in SmtpClient.NoOp() and NoOpAsync() methods.
• Improved default SSL certificate validation logic to be more secure and to recognize the most commonly used mail servers even if their Root CA Certificates are not available on the system.
• SslHandshakeException's Message has been improved to be based on the errors reported in the ServerCertificateValidationCallback and also now has 2 new X509Certificate properties which represent the ServerCertificate and the RootCertificateAuthority in order to help developers diagnose problems. (issue #1002)
• Improved the IMAP PreviewText to extract text from HTML bodies. (issue #1001)
• Renamed MessageSummaryItems.Id to MessageSummaryItems.EmailId to better map to the property name used in the IMAP OBJECTID specification.
• Updated NetworkStream.ReadAsync() and WriteAsync() methods to make use of timeouts. (issue #827)

• Added work-around for ENVELOPE responses with a NIL address token in an address-list. (issue #991)

• Fixed the IMAP ENVELOPE parser to have a more lenient fallback if it fails to be able to parse the Message-Id token value. (issue #976)
• Fixed MailService.DefaultServerCertificateValidationCallback() to compare certificates by their hashes rather than via Object.Equals(). (issue #977)
• Added work-around for IMAP servers that send -1 as a line count or octet count in the BODYSTRUCTURE response.

• Ignore NIL tokens in the body-fld-lang token list. (issue #953)
• Added logic to handle unexpected <CR><LF> in untagged FETCH responses. (issue #954)
• Added a way to override SmtpClient's preference for using BDAT vs DATA via a new PreferSendAsBinaryData virtual property.
• Update SslHandshakeException message to mention the possibility of SSL/TLS version mismatch. (issue #957)
• Fixed ImapFolder.GetStreamsAsync() to use an async callback delegate. (issue #958)
• Added protocol-specific interfaces that inherit from IMailFolder, IMailStore, etc. (issue #960)
• Maintain the STARTTLS capability bit flag after a STARTTLS command.
• Don't send the optional ANNOTATE parameter to SELECT/EXAMINE for SUN IMAP servers (such as Apple's IMAP servers). (issue #970)

Note: Developers using ImapFolder.GetStreamsAsync() will need to update their code as this release breaks API/ABI.

• Don't use PublicSign on non-Windows NT machines when building.
• Work-around broken BODYSTRUCTUREs with () as a message/rfc822 body token. (issue #944)
• Added work-around for an Exchange bug that forgets to quote folder names containing tabs. (issue #945)
• Moved the SmtpDataFilter into the public API and updated the FAQ to show how to use it when writing messages into an IIS "pickup directory". (issue #948)

• Added work-around for IMAP ENVELOPE responses that do not include an In-Reply-To token. (issue #932)
• Dropped support for WindowsPhone/Universal v8.1.
• Added a net48 assembly to the NuGet package which supports TLS v1.3.
• Added work-around for Yandex IMAP servers to disconnect immediately upon * BYE. (issue #938)
• Fixed ImapClient.Idle() and IdleAsync(). (issue #942)
• Added work-around for Lotus Domino where it adds extra ()'s around some FETCH items. (issue #943)

• Fixed trimming delimiters from the end of IMAP folder names.
• Fixed fetching of IMAP PreviewText when message bodies do not contain any text parts.
• Fixed Pop3Client to never emit Authenticated events w/ null messages.
• Dropped SslProtocols.Tls (aka TLSv1.0) from the default SslProtocols used by IMAP, POP3 and SMTP clients. To override this behavior, use the client.SslProtocols property to set the preferred SslProtocol(s).
• Fixed ImapFolder.Search(string query) to properly encode the query string when the query contains unicode characters.
• If an IMAP SEARCH fails due to BADCHARSET, retry the search query after flattening the query strings into US-ASCII. This may fix issues such as issue #808.
• Added work-arounds for Exchange IMAP bugs causing it to send mal-formed body-fld-dsp parameters. (issue #919)
• Go back to only using the BDAT command when the user is sending BINARYMIME in the SmtpClient. (issue #921)

• Fixed SmtpClient.Send*() to make sure never to add an extra CRLF sequence to the end of messages when sending via the DATA command. (issue #895)
• Added assemblies for net46 and net47 to the NuGet package.

• Improved the default SSL/TLS certificate validation logic.
• Improved exception messages for the POP3 LIST and STAT commands.
• Modified Pop3Client to accept negative values for the 'octets' value in the STAT response. (issue #872)
• Added work-around for IMAP BODYSTRUCTURE responses that treat multiparts as basic parts. (issue #878)
• Added check to make sure that MD5 is supported by the runtime and automatically disable support for CRAM-MD5 and DIGEST-MD5 SASL mechanisms when MD5 is not supported.
• Added a Stream property to ProtocolLogger.
• Fixed fetching of PreviewText items if the body's ContentTransferEncoding is NIL. (issue #881)
• Improved processing of pipelined SMTP commands to provide better exception messages. (issue #883)
• Modified SmtpClient.Send*() to not call MimeMessage.Prepare() if any DKIM or ARC headers are present in order to avoid the potential risk of altering the message and breaking the signatures within those headers.
• Added SmtpClient.SendCommand() and SendCommandAsync() to allow custom subclasses the ability to send custom commands to the SMTP server. (issue #891)
• Allow SmtpClient subclasses to override message preparation by overriding a new SmtpClient.Prepare() method. (issue #891)
• Improved ImapFolder's ModSeqChanged event to set the UniqueId property if available in unsolicited FETCH notifications including a MODSEQ and UID value.
• Fixed the IMAP client logic to properly handle lower or mixed case IMAP tokens. (issue #893)
• Added support for IMAP's ANNOTATE-EXPERIMENT-1 extension. (issue #818)
• Always use the SMTP BDAT command instead of DATA if CHUNKING is supported. (issue #896)
• Improved SmtpClient to include a SIZE= parameter in the MAIL FROM command if the SIZE extension is supported. Progress reporting will now always have the expected message size available as well.

• Optimized MailKit's logic for breaking apart long IMAP commands for GMail, Dovecot, and Yahoo! Mail.
• Fixed the IMAP stream tokenizer to properly handle UTF8 atom tokens. (issue #859)
• Fixed IMAP search code to always handle untagged SEARCH responses even when the response SHOULD be an untagged ESEARCH response. (issue #863)
• Replaced SearchQuery.SentAfter with SentSince to be more consistent with IMAP terminology.

• Bumped the System.Net.Security dependency for security fixes (CVE-2017-0249).
• Reduced explicit nuget dependencies.
• Added a work-around for Microsoft Exchange IMAP servers that sometimes erroneously respond with unneeded continuation responses. (issue #852)
• Fixed the ImapClient to Stop looping over SASL mechanisms if the server disconnects us. (issue #851)
• Added support for HTTP proxies. (issue #847)
• Fixed IMAP to properly handle EXPUNGE notifications during a FETCH request. (issue #850)

• Fixed ImapUtils.GetUniqueHeaders() to accept all valid header field name characters. (issue #806)
• Catch all exceptions thrown in IdleComplete(). (issue #825)
• Improved cancellability of IMAP, POP3 and SMTP clients when sending commands to the server. (issue #827)
• Break apart IMAP commands with really long uid-sets. (issue #834)
• Rewrote Connect logic to use Socket.Connect (IPAddress, int) instead of Connect (string, int) in an attempt to fix StackOverflow 87117
• Fixed SmtpStream.ReadAheadAsync() to preserve remaining input. (issue #842)

• Fixed IMAP GetFolder() methods to match LIST responses case-insensitively. (issue #803)
• Added a work-around to SmtpClient for a .NET 4.5.2 bug on Windows 7 SP1. (issue #814)
• Added DeliveryStatusNotificationType and a property to SmtpClient to allow developers to specify the RET parameter value to the MAIL FROM command.
• Fixed a number of locations in the code to clear password buffers after using them.
• SmtpClient.Send() and SendAsync() methods that accept a FormatOptions argument will no longer hide Bcc, Resent-Bcc, nor Content-Length headers when uploading the raw message to the SMTP server. It is now up to callers to add these values to their custom FormatOptions.HiddenHeaders property. (issue #360)