MailKit

• A number of fixes to bugs exposed in new unit tests for NTLM authentication.
• Made SmtpClient, Pop3Client, and ImapClient's Connect() methods truly cancellable as well as made the underlying socket.Connect() call adhere to any specified client.Timeout value.
• Added support for connecting via a SOCKS4, SOCKS4a, or SOCKS5 proxy server.
• Fixed ImapClient's OnAuthenticated() method to protect against throwing an ArgumentNullException when trying to emit the Authenticated event if the server did not supply any resp-code-text in the OK response to the AUTHENTICATE command. (issue #774)
• Modified ImapFolder.Create() to handle [ALREADYEXISTS] resp-codes.
• Fixed ImapFolder.Create() for GMail when the isMessageFolder parameter is false (GMail doesn't handle it when the client attempts to create a folder ending with a directory separator).
• Optimized ImapFolder's fallback for UID COPY command when UIDPLUS is not supported.
• Reduced string allocations in the Connect(Uri) wrapper.
• Added new ConnectedEventArgs and DisconnectedEventArgs that are used with the Connected and Disconnected events to provide developers with even more useful information about what server, port and SecureSocketOptions were used when connecting the client.
• Fixed SmtpClient to immediately throw stream reading exceptions instead of ignoring them. (issue #776)
• Fixed ImapClient.GetFoldersAsync() to call ImapFolder.StatusAsync() instead of Status() when StatusItems are specified.
• Changed ImapFolder.GetSubfolders() to return IList<IMailFolder> instead of IEnumerable<IMailFolder>.
• Fixed ImapClient's NAMESPACE parser - it had Shared and Other namespace ordering reversed.
• Fixed ImapFolder.Create() (for special-use) to only use unique uses if any were specified multiple times.
• Modified ImapFolder.Open() to allow devs to re-Open() a folder with the same access in case they need to do this to work around an IMAP server bug(?).
• Fixed adding/removing/setting of GMail labels to use UTF-8 when enabled.
• Added support for the IMAP STATUS=SIZE extension which now provides a ImapFolder.Size property that specifies how large a folder is (in bytes). Clients can request this information using the StatusItems.Size enum with either ImapFolder.GetSubfolders() or ImapFolder.Status().
• Added support for the IMAP OBJECTID extension. ImapFolder and IMessageSummary now both have an Id property which is a globally unique identifier. IMessageSummary also now has a ThreadId property which is a unique identifier for the message thread/conversation that the message belongs to. This information can be retrieved for ImapFolders using ImapFolder.Status() with the new StatusItems.MailboxId enum value. The IMessageSummary.Id and ThreadId properties have the corresponding MessageSummaryItems enum values of Id and ThreadId, respectively.
• Added another work-around for bad GMail IMAP BODYSTRUCTURE responses. (issue #777)
• Fixed all integer TryParse methods to use NumberStyles.None and CultureInfo.InvariantCulture.
• Added Connect() and ConnectAsync() overloads which accept a Stream instead of a Socket.
• All ImapFolder.MessageFlagsChanged, ModSeqChanged, and LabelsChanged events will now also be followed by a MessageSummaryFetched event containing the combined information of those events.
• Added support for IMAP's NOTIFY extension. Many thanks to Steffen Kieß for getting the ball rolling on this feature by implementing the necessary ImapEvent, ImapEventGroup, and ImapMailboxFilter classes as well as the initial support.

API Changes Since 2.0.x:

• Obsoleted SearchQuery.HasCustomFlags() and SearchQuery.DoesNotHaveCustomFlags(). These are now SearchQuery.HasKeywords() and SearchQuery.NotKeywords(), respectively.
• Obsoleted SearchQuery.DoesNotHaveFlags() in favor of SearchQuery.NotFlags().
• Obsoleted the IMessageSummary.UserFlags property in favor of IMessageSummary.Keywords.
• Obsoleted the MessageFlagsChangedEventArgs.UserFlags property in favor of MessageFlagsChangedEventArgs.Keywords.
• All IMailFolder.Fetch and IMailFolder.FetchAsync methods that took a HashSet<string> userFlags argument now take an IEnumerable<string> keywords argument. Note: this only affects you if your code used named method parameters (e.g. userFlags: myUserFlags).

• Added a work-around for Exchange IMAP servers that send broken multipart BODYSTRUCTURE responses without a body-fld-dsp token.
• Added support for detecting (but not using) the UNAUTHENTICATE IMAP extension.
• Reintroduced the Pop3Client.GetMessageCount() and GetMessageCountAsync() methods to allow developers to poll POP3 servers for new messages. (issue #762)
• Fixed SmtpClient's status code logic to handle more than the expected error codes for the MAIL FROM and RCPT TO commands. (issue #764)
• Added a work-around for IMAP servers that quote FLAGS responses. (issue #771)
• Optimized SmtpClient's logic for byte-stuffing the message when writing it to the socket during the DATA command.
• Added an SslProtocols property to IMailService (was already in MailService).
• Fixed the DIGEST-MD5 charset handling.
• Fixed a bug in the BodyPart.TryParse() method that could be used when serializing and deserializing FETCH'd responses from an IMAP server.
• Fixed BodyPartCollection.IndexOf(Uri).
• Fixed Envelope.ToString() and TryParse() to properly deal with the rfc822 group address syntax.
• Fixed the ImapClient logic to properly handle parsing nested group addresses (not likely that anyone would hit this).
• Improved ImapClient's state tracking so that it is possible to re-connect the ImapClient in the Disconnected event handler. (issue #770)
• Fixed IMAP API's that take IList of UIDs or indexes to accept 0 UIDs/indexes.
• Fixed ImapClient's BODYSTRUCTURE parser to properly handle multiple body-extensions tokens.
• Fixed ImapClient to properly handle the * PREAUTH greeting when connecting to an IMAP server.

• Fixed ImapFolder.GetSubfolders (StatusItems) to make sure that the child folders exist before calling STATUS on them when the server does not support the LIST-STATUS command.
• Catch ArgumentExceptions when calling Encoding.GetEncoding(string). (issue #740)
• Fixed parsing of IMAP threads where the root of a subtree is empty. (issue #739)
• Added AuthorizationId property for PLAIN and DIGEST-MD5 SASL mechanisms.
• Added MessageSummaryItems.Headers enum to fetch all headers. (issue #738)

• When throwing AuthenticationException within SmtpClient, add an SmtpCommandException as the InnerException property to help consumers diagnose authentication problems. (issue #717)
• Added support for the authzid to the SASL PLAIN mechanism.
• Modified ProtocolLogger file constructor to support Shared Read and an Append/Overwrite option. (issue #730)

• Fixed SmtpClient to use the IPv4 literal if the socket is IPv4 address mapped to IPv6. (issue #704)
• Updated SmtpClient and ImapFolder.Append to use FormatOptions.EnsureNewLine. (MimeKit issue #251)

• Fixed IMAP IDLE support.
• Ignore unknown tokens in IMAP untagged FETCH responses such as XAOL.SPAM.REASON.

• Added work-around for ProtonMail's IMAP server. (issue #674)
• Added work-around for IMAP servers that do not include msgid in the ENVELOPE response. (issue #669)
• Added MessageSummaryItems.PreviewText to allow fetching a small preview of the message. (issue #650)
• Added support for batch fetching IMAP message streams. (issue #650)

• Obsoleted all SaslMechanism constructors that took a Uri argument and replaced them with variants that no longer require the Uri and instead take a NetworkCredential or a set of strings for the user name and password. This simplifies authenticating with OAuth 2.0:

var oauth2 = new SaslMechanismOAuth2 (username, auth_token);

client.Authenticate (oauth2);

• Updated MailKit to fully support async IO instead of using Task.Run() wrappers.
• Fixed a resource leak when fetching IMAP body parts gets an exception.
• Fixed each of the Client.Connect() implementations to catch exceptions thrown by IProtocolLogger.LogConnect().
• Removed the ImapFolder.MessagesArrived event.
• Added new Authenticate() methods that take a SaslMechanism to avoid the need to manipulate Client.AuthenticationMechanisms in order to tweak which SASL mechanisms you'd like the client to use in Authenticate().
• Added new SslHandshakeException with a helpful error message that can be thrown by the Connect() methods. This replaces the obscure SocketExceptions previously thrown by SslStream.
• Fixed support for the IMAP UTF8=ACCEPT extension.
• Improved ImapFolder.CommitStream() API to provide section, offset and length.
• Treat the SMTP X-EXPS capability in an EHLO response the same as AUTH. (issue #603)
• Dropped support for .NET 4.0.

Note: As of 2.0, XOAUTH2 is no longer in the list of SASL mechanisms that is tried when using the Authenticate() methods that have existed pre-MailKit 2.0. Instead, you must now use Authenticate(SaslMechanism, CancellationToken).

An example usage might look like this:

// Note: The Uri isn't used except with ICredentials.GetCredential (Uri) so unless
// you implemented your own ICredentials class, the Uri is a dummy argument.
var uri = new Uri ("imap://imap.gmail.com");
var oauth2 = new SaslMechanismOAuth2 (uri, username, auth_token);

client.Authenticate (oauth2);

• Enable TLSv1.1 and 1.2 for .NETStandard.
• Read any remaining literal data after parsing headers. Fixes an issue when requesting specific headers in an ImapFolder.Fetch() request if the server sends an extra newline.

• Fixed UniqueIdRange.ToString() to always output a string in the form ${start}:${end} even if start == end. (issue #572)

• Gracefully handle IMAP COPYUID resp-codes without src or dest uid-set tokens. (issue #555)
• Be more lenient with unquoted IMAP folder names containing ']'. (issue #557)

• Improved logic for cached FolderAttributes on ImapFolder objects.
• If/when the \NonExistent flag is present, reset ImapFolder state as it probably means another client has deleted the folder.
• Added work-around for home.pl which sends an untagged * [COPYUID ...] response without an OK (technically, the COPYUID resp-code should only appear in the tagged response, but accept it anyway).

• Added a leaveOpen param to the ProtocolLogger .ctor. (issue #506)
• Added a CheckCertificateRevocation property on MailService. (issue #520)
• Fixed ImapFolder to update the Count property and emit CountChanged when the IMAP server sends an untagged VANISHED response. (issue #521)
• Fixed ImapEngine to properly handle converting character tokens into strings. (issue #522)
• Fixed SmtpClient to properly handle DIGEST-MD5 auth errors in order to fall back to the next authentication mechanism.
• Fixed Pop3Client to properly detect APOP tokens after arbitrary text. (issue #529)
• Disabled NTLM authentication since it often doesn't work properly. (issue #532)

• Properly handle a NIL body-fld-params token for body-part-mpart. (issue #503)

• Improved IMAP ENVELOPE parser to prevent exceptions when parsing invalid mailbox addresses. (issue #494)
• Fixed UniqueId and UniqueIdRange to prevent developers from creating invalid UIDs and ranges.
• Fixed ImapFolder.FetchStream() to properly emit MODSEQ changes if the server sends them.
• Fixed SmtpClient to call OnNoRecipientsAccepted even in the non-PIPELINE case. (issue #491)

• Improved IMAP's BODYSTRUCTURE parser to sanitize the Content-Disposition values. (issue #486)
• Improved robustness of IMAP's BODYSTRUCTURE parser in cases where qstring tokens have unescaped quotes. (issue #485)
• Fixed IMAP to properly handle NIL as a folder name in LIST, LSUB and STATUS responses. (issue #482)
• Added ImapFolder.GetHeaders() to allow developers to download the entire set of message headers.
• Added SMTP support for International Domain Names in email addresses used in the MAIL FROM and RCPT TO commands.
• Modified SmtpClient to no longer throw a NotSupportedException when trying to send messages to a recipient with a unicode local-part in the email address when the SMTP server does not support the SMTPUTF8 extension. Instead, the local-part is passed through as UTF-8, leaving it up to the server to reject either the command or the message. This seems to provide the best interoperability.

• Allow an empty string text argument for SearchQuery.ContainsHeader(). (issue #451)
• Fixed SaslMechanism.IsProhibited() logic to properly use logical ands. Thanks to Stefan Seering for this fix.

• Added an IsAuthenticated property to IMailService.
• Fixed the ImapFolder.Quota class to not be public.

• Modified the ImapClient to always LIST the INBOX even if it is a namespace in order to get any flags set on it.
• Fixed ImapFolder to handle Quota Roots that do not match an existing folder. (issue #433)
• Added work-around for Courier-IMAP sending "* 0 FETCH ..." on flag changes. (issue #428)
• Updated MessageSorter to be smarter about validating arguments such that it will only check for IMessageSummary fields that it will actually need in order to perform the specified sort.
• Fixed SmtpClient.Authenticate() to throw an AuthenticationException with a message from the SMTP server if available.

• Added SearchQuery.Uids() to allow more powerful search expressions involving sets of uids.
• Changed ImapClient.GetFolders() to return IList instead of IEnumerable.
• Fixed a bug in MessageThreader.
• Fixed bugs in Envelope.ToString() and Envelope.TryParse().
• Fixed NTLM's Type2Message.Encode() logic to properly handle a null TargetInfo field.
• Obsoleted some ImapFolder.Search() methods and replaced them with an equivalent ImapFolder.Sort() method.
• Added a ResponseText property to ImapCommandException.
• Fixed ImapFolder to emit a HighestModSeqChanged event when we get untagged FETCH responses with a higher MODSEQ value.
• Improved SearchQuery optimization for IMAP.
• Added SearchOptions.None.

• Fixed the NuGet packages to reference MimeKit 1.8.0.
• Added an SmtpClient.QueryCapabilitiesAfterAuthenticating property to work around broken SMTP servers where sending EHLO after a successful AUTH command incorrectly resets their authenticated state.

• Added a new Search()/SearchAsync() to ImapFolder that take a raw query string.
• Implemented support for the IMAP FILTERS extension and improved support for the METADATA extension.
• Fixed NTLM authentication support to use NTLMv2. (issue #397)
• Added support for IMAP's SEARCH=FUZZY relevancy scores.
• Added an IMailFolder.ModSeqChanged event.
• Added UniqueIdRange.All for convenience.

• Added support for the new IMAP LITERAL- extension.
• Added support for the new IMAP APPENDLIMIT extension.
• Fixed APOP authentication in the Pop3Client. (issue #395)
• Reset the SmtpClient's Capabilities after disconnecting.
• Modified ImapFolder.Search() to return a UniqueIdSet for IMAP servers that do not support the ESEARCH extension (which already returns a UniqueIdSet).
• Added mail.shaw.ca to the list of SMTP servers that break when sending EHLO after AUTH. (issue #393)
• Work around broken POP3 servers that reply "+OK" instead of "+" in SASL negotiations. (issue #391)
• Modified the IMAP parser to properly allow "[" to appear within flag tokens. (issue #390)

• Properly initialize the private Uri fields in Connect() for Windows Universal 8.1. (issue [#381, #382](https://github.com/jstedfast/MailKit/issues/381, #382))
• Added SecuritySafeCritical attributes to try and match base Exception in case that matters.
• Added missing GetObjectData() implementation to Pop3CommandException.
• Strong-name the .NET Core assemblies.
• Make sure to process Alert resp-codes in ImapClient. (issue #377)

• Updated the NTLM SASL mechanism to include a Windows OS version in the response if the server requests it (apparently this should only happen if the server is in debug mode).
• Updated the IMAP BODYSTRUCTURE parser to try and work around BODYSTRUCTURE responses that do not properly encode the mime-type of a part where it only provides the media-subtype token instead of both the media-type and media-subtype tokens. (issue #371)
• Added smtp.dm.aliyun.com to the list of broken SMTP servers that failed to read the SMTP specifications and improperly reset their state after sending an EHLO command after authenticating (which the specifications explicitly state the clients SHOULD do). (issue #370)

• Added support for .NET Core 1.0

• Fixed logic for constructing the HELO command on WP8. (issue #351)
• Modified ImapFolder.Search() to not send the optional CHARSET search param if the charset is US-ASCII. This way work around some broken IMAP servers that do not properly implement support for the CHARSET parameter. (issue #348)
• Added more MailService methods to IMailService.

• Properly apply SecurityCriticalAttribute to GetObjectData() on custom Exceptions. (issue #340)

• Updated IMAP BODY parser to handle a NIL media type by treating it as "application".
• Updated IMAP SEARCH response parser to work around search-return-data pairs within parens.
• Added a missing SmtpStatusCode enum value for code 555. (issue #327)
• Opened up more of the SearchQuery API to make it possible to serialize/deserialize via JSON. (issue #331)
• Updated to reference BouncyCastle via NuGet.org packages rather than via project references.

• Replaced SmtpClient's virtual ProcessRcptToResponse() method with OnRecipientAccepted() and OnRecipientNotAccepted(). (issue #309)
• Added MailService.DefaultServerCertificateValidationCallback() which accepts all self-signed certificates (a common operation that consumers want).
• Fixed encoding and decoding of IMAP folder names that include surrogate pairs.
• Fixed IMAP SEARCH logic for X-GM-LABELS.

• Added a work-around for GoDaddy's ASP.NET web host which does not support the iso-8859-1 System.Text.Encoding (used as a fallback encoding within MailKit) by falling back to Windows-1252 instead.
• Improved NTLM support.

• Added support for the SMTP VRFY and EXPN commands.

• If the IMAP server sends a * ID NIL response, return null for ImapClient.Identify().
• Allow developers to override the charset used when authenticating. (issue #292)

• Exposed MailKit.Search.OrderByType and MailKit.Search.SortOrder to the public API.
• Modified IMailFolder.CopyTo() and MoveTo() to return a UniqueIdMap instead of a UniqueIdSet.
• Improved ImapProtocolException error messages to be more informative.
• Added an IsSecure property to ImapClient, Pop3Client and SmtpClient.
• Fixed support for the IMAP COMPRESS=DEFLATE extension to work properly.
• Modified UniqueId.Id and .Validity to be properties instead of fields.
• Reduced memory usage for UniqueIdRange (-33%) and UniqueIdSet (-50%).
• Vastly improved the performance of UniqueIdSet (~2x).
• Added an ImapClient.GetFolders() overload that also requests the status of each folder.
• Modified the headersOnly parameter to the various Pop3Client.GetStream() methods to default to false instead of forcing developers to pass in a value.
• Updated the IMAP, POP3 and SMTP clients to be stricter with validating SSL certificates.

• Added support for the SCRAM-SHA-256 SASL mechanism.
• Added support for the CREATE-SPECIAL-USE IMAP extension.
• Added support for the METADATA IMAP extension.
• Added support for the LIST-STATUS IMAP extension.

• Be more forgiving during SASL auth when a POP3 server sends unexpected text after a + response. (issue #268)

• Fixed ImapFolder.Search() to not capitalize the date strings in date queries. (issue #252)
• Fixed filtering logic in ImapFolder.GetSubfolders() to not filter out subfolders named Inbox. (issue #255)
• Exposed SmtpClient.ProcessRcptToResponse() as virtual protected to allow subclasses to override error handling. (issue #256)
• Modified SmtpCommandException .ctors to be public and fixed serialization logic. (issue #257)
• Added workaround for broken smtp.sina.com mail server.
• Throw a custom ImapProtocolException on "* BYE" during connection instead of "unexpected token". (issue #262)

• Fixed SmtpClient to not double dispose the socket.
• Added a BodyPartVisitor class.
• Fixed ImapFolder to allow NIL tokens for body parts. (issue #244)

• Allow developers to specify a local IPEndPoint to use for connecting to remote servers. (issue #247)
• Added support for NIL GMail labels. (issue #244)

• Fixed SmtpStream logic for determining if a call to ReadAhead() is needed. (issue #232)
• Fixed ImapFolder.Close() to change the state to Closed even if the IMAP server does not support the UNSELECT command.
• Allow the UIDVALIDITY argument to the COPYUID and APPENDUID resp-codes to be 0 even though that value is illegal. Improves compatibility with SmarterMail. (issue #240)

• Added an SslProtocols property to ImapClient, Pop3Client, and SmtpClient to allow developers to override which SSL protocols are to be allowed for SSL connections. (issue #229)
• Added a work-around for GMail IMAP (and other IMAP servers) that sometimes send an illegal MODSEQ value of 0. (issue #228)

• Fixed ImapFolder.Append() methods to make sure to encode the message with <CR><LF> line endings.
• Added UniqueId.Invalid that can be used for error conditions.
• Added UniqueId.IsValid property to check that the UniqueId is valid.
• Added Opened and Closed events to IMailFolder.
• Fixed the QRESYNC version of the IMailFolder.Open() method to take a uint uidValidity instead of a UniqueId uidValidity argument for consistency.
• Updated MessageSorter.Sort() to be an extension method and added a List<T> overload.
• Updated MessageThreader.Thread() to be extension methods (required reordering of args).
• Merged ISortable and IThreadable interfaces into IMessageSummary in order to remove duplicated properties and simplify things.
• Renamed IMessageSummary.MessageSize to IMessageSummary.Size.
• Modified IMessageSummary.UniqueId to no longer be nullable.
• Added TextBody, HtmlBody, BodyParts and Attachments properties to IMessageSummary.
• Modified the IMAP parser to allow NIL for the Content-Type and subtype strings in BODY and BODYSTRUCTURE values even though it is illegal. (issue #226)
• Modified the IMAP parser to properly handle Message-Id tokens that are not properly encapsulated within angle brackets. (issue #224)
• Fixed IMAP to properly deal with folder names that contained unescaped square brackets. (issue #222)

• Fixed ImapFolder to dispose the temporary streams used in GetMessage and GetBodyPart.
• Added a MessageNotFoundException.
• Added an ImapCommandResponse property to ImapCommandException.
• Fixed SmtpClient to filter out duplicate recipient addresses in RCPT TO.
• Modified MessageSorter/Threader to take IList<OrderBy> arguments instead of OrderBy[].
• Added support for parsing group addresses in IMAP ENVELOPE responses.
• Disable SASL-IR support for the LOGIN mechanism. (issue #216)
• Capture whether or not the IMAP server supports the I18NLEVEL and LANGUAGE extensions.

• Fixed ImapFolder.Rename() to properly emit the Renamed event for child folders as well.
• Fixed ImapFolder.Fetch() to always fill in the Headers property when requesting specific headers even if the server replies with an empty list. (issue #210)