I created some code in C# to read the email from a folder on my (local/NAS) IMAP server. Code is not finished, but in the end I would like to have a list of all the mailsubjects.

The response from below code is:

Total messages: 93
MessageError 0: The IMAP server has unexpectedly disconnected.

This question: "The IMAP server has unexpectedly disconnected" using 993 port and MailKit did not solve the problem, because I also had it when accessing via port 993, and now via port 143 i still have the same problem.

When checking that folder using Thunderbird I do see those 93 messages (and I am able to read those messages).

Any help would be appreciated to be able to read those messages.

public static void CheckIMAP()
{
    using (var client = new ImapClient(new ProtocolLogger(@"d:\temp\imap.log")))
    {
        //client.Connect(mailserver, 993, true);
        client.Connect(mailserver, 993, SecureSocketOptions.SslOnConnect);
        //client.Connect(mailserver, 143, SecureSocketOptions.None);

        client.Authenticate(username, password);

        IMailFolder folder = client.GetFolder("INBOX.subfolder");
        var fo = folder.Open(FolderAccess.ReadOnly);
        Console.WriteLine ("Total messages: {0}", folder.Count);
        for (int i = 0; i < folder.Count; i++)
        {
            try
            {
                var message = folder.GetMessage(i);
                Console.WriteLine("Message: {0}", message.Subject);
            }
            catch (Exception ex)
            {
                System.Console.WriteLine($"MessageError {i}: {ex.Message}");
                break;
            }
        }
        System.Console.WriteLine();

        client.Disconnect(true);
    }
}

The end result of this program should be almost (because date of the message should also be in the result, but that's not the question right now ) the same as this Linux command running on my NAS:

$ grep '^Subject:' ~/.Maildir/.INBOX.subfolder/cur/*

Versions:

Mailkit: 4.10.0; Dotnet: 9.0.200

Developing on Windows 11, when finished it should run under Linux (on my Synology NAS)

EDIT:

The contents of the imap.log:

Connected to imaps://example:993/
S: * OK [CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+ AUTH=PLAIN] Dovecot ready.
C: A00000000 AUTHENTICATE PLAIN ********
S: A00000000 OK [CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS THREAD=ORDEREDSUBJECT MULTIAPPEND URL-PARTIAL CATENATE UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS BINARY MOVE SNIPPET=FUZZY PREVIEW=FUZZY PREVIEW STATUS=SIZE SAVEDATE LITERAL+ NOTIFY SPECIAL-USE] Logged in
C: A00000001 NAMESPACE
S: * NAMESPACE (("" ".")) NIL NIL
S: A00000001 OK Namespace completed (0.001 + 0.000 secs).
C: A00000002 LIST "" "INBOX" RETURN (SUBSCRIBED CHILDREN)
S: * LIST (\Subscribed \HasChildren) "." INBOX
S: A00000002 OK List completed (0.076 + 0.000 + 0.075 secs).
C: A00000003 LIST (SPECIAL-USE) "" "*" RETURN (SUBSCRIBED CHILDREN)
S: * LIST (\Subscribed \HasNoChildren \UnMarked \Drafts) "." Drafts
S: * LIST (\Subscribed \HasNoChildren \Sent) "." Sent
S: * LIST (\Subscribed \HasNoChildren \UnMarked \Junk) "." Junk
S: * LIST (\Subscribed \HasNoChildren \UnMarked \Trash) "." Trash
S: A00000003 OK List completed (0.007 + 0.000 + 0.006 secs).
C: A00000004 LIST "" INBOX.subfolder RETURN (SUBSCRIBED CHILDREN)
S: * LIST (\Subscribed \HasNoChildren) "." INBOX.subfolder
S: A00000004 OK List completed (0.007 + 0.000 + 0.006 secs).
C: A00000005 EXAMINE INBOX.subfolder (CONDSTORE)
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS ()] Read-only mailbox.
S: * 93 EXISTS
S: * 0 RECENT
S: * OK [UIDVALIDITY 1516544306] UIDs valid
S: * OK [UIDNEXT 103] Predicted next UID
S: * OK [HIGHESTMODSEQ 158] Highest
S: A00000005 OK [READ-ONLY] Examine completed (0.005 + 0.000 + 0.004 secs).
C: A00000006 FETCH 1 (BODY.PEEK[])
S: * 1 FETCH (BODY[] {950}
S: Return-Path: <[email protected]>
S: X-Original-To: [email protected]
S: Delivered-To: [email protected]
S: Received: from <obfuscated>
S:  (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits)
S:   key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256)
S:  (No client certificate requested)
S:  by example (Postfix) with ESMTPSA id BB6801EF0A5
S:  for <[email protected]>; Thu, 11 Apr 2024 20:14:49 +0200 (CEST)
S: X-Is-Generated-Message-Id: true
S: MIME-Version: 1.0
S: Content-Transfer-Encoding: quoted-printable
S: Content-Type: text/plain;
S:  charset=UTF-8
S: Subject: <obfuscated>
S: From: Luuk <[email protected]>
S: Date: Thu, 9 Apr 2024 20:14:48 +0200
S: To: [email protected]
S: Message-ID: <[email protected]>
S: X-MailScanner-ID: BB6801EF0A5.A5150
S: X-MailScanner: Found to be clean
S: X-MailScanner-From: [email protected]
S: X-Spam-Status: No
S: 
S: 

I created some code in C# to read the email from a folder on my (local/NAS) IMAP server. Code is not finished, but in the end I would like to have a list of all the mailsubjects.

The response from below code is:

Total messages: 93
MessageError 0: The IMAP server has unexpectedly disconnected.

This question: "The IMAP server has unexpectedly disconnected" using 993 port and MailKit did not solve the problem, because I also had it when accessing via port 993, and now via port 143 i still have the same problem.

When checking that folder using Thunderbird I do see those 93 messages (and I am able to read those messages).

Any help would be appreciated to be able to read those messages.

public static void CheckIMAP()
{
    using (var client = new ImapClient(new ProtocolLogger(@"d:\temp\imap.log")))
    {
        //client.Connect(mailserver, 993, true);
        client.Connect(mailserver, 993, SecureSocketOptions.SslOnConnect);
        //client.Connect(mailserver, 143, SecureSocketOptions.None);

        client.Authenticate(username, password);

        IMailFolder folder = client.GetFolder("INBOX.subfolder");
        var fo = folder.Open(FolderAccess.ReadOnly);
        Console.WriteLine ("Total messages: {0}", folder.Count);
        for (int i = 0; i < folder.Count; i++)
        {
            try
            {
                var message = folder.GetMessage(i);
                Console.WriteLine("Message: {0}", message.Subject);
            }
            catch (Exception ex)
            {
                System.Console.WriteLine($"MessageError {i}: {ex.Message}");
                break;
            }
        }
        System.Console.WriteLine();

        client.Disconnect(true);
    }
}

The end result of this program should be almost (because date of the message should also be in the result, but that's not the question right now ) the same as this Linux command running on my NAS:

$ grep '^Subject:' ~/.Maildir/.INBOX.subfolder/cur/*

Versions:

Mailkit: 4.10.0; Dotnet: 9.0.200

Developing on Windows 11, when finished it should run under Linux (on my Synology NAS)

EDIT:

The contents of the imap.log:

Connected to imaps://example:993/
S: * OK [CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE LITERAL+ AUTH=PLAIN] Dovecot ready.
C: A00000000 AUTHENTICATE PLAIN ********
S: A00000000 OK [CAPABILITY IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS THREAD=ORDEREDSUBJECT MULTIAPPEND URL-PARTIAL CATENATE UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS BINARY MOVE SNIPPET=FUZZY PREVIEW=FUZZY PREVIEW STATUS=SIZE SAVEDATE LITERAL+ NOTIFY SPECIAL-USE] Logged in
C: A00000001 NAMESPACE
S: * NAMESPACE (("" ".")) NIL NIL
S: A00000001 OK Namespace completed (0.001 + 0.000 secs).
C: A00000002 LIST "" "INBOX" RETURN (SUBSCRIBED CHILDREN)
S: * LIST (\Subscribed \HasChildren) "." INBOX
S: A00000002 OK List completed (0.076 + 0.000 + 0.075 secs).
C: A00000003 LIST (SPECIAL-USE) "" "*" RETURN (SUBSCRIBED CHILDREN)
S: * LIST (\Subscribed \HasNoChildren \UnMarked \Drafts) "." Drafts
S: * LIST (\Subscribed \HasNoChildren \Sent) "." Sent
S: * LIST (\Subscribed \HasNoChildren \UnMarked \Junk) "." Junk
S: * LIST (\Subscribed \HasNoChildren \UnMarked \Trash) "." Trash
S: A00000003 OK List completed (0.007 + 0.000 + 0.006 secs).
C: A00000004 LIST "" INBOX.subfolder RETURN (SUBSCRIBED CHILDREN)
S: * LIST (\Subscribed \HasNoChildren) "." INBOX.subfolder
S: A00000004 OK List completed (0.007 + 0.000 + 0.006 secs).
C: A00000005 EXAMINE INBOX.subfolder (CONDSTORE)
S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft)
S: * OK [PERMANENTFLAGS ()] Read-only mailbox.
S: * 93 EXISTS
S: * 0 RECENT
S: * OK [UIDVALIDITY 1516544306] UIDs valid
S: * OK [UIDNEXT 103] Predicted next UID
S: * OK [HIGHESTMODSEQ 158] Highest
S: A00000005 OK [READ-ONLY] Examine completed (0.005 + 0.000 + 0.004 secs).
C: A00000006 FETCH 1 (BODY.PEEK[])
S: * 1 FETCH (BODY[] {950}
S: Return-Path: <[email protected]>
S: X-Original-To: [email protected]
S: Delivered-To: [email protected]
S: Received: from <obfuscated>
S:  (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits)
S:   key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256)
S:  (No client certificate requested)
S:  by example (Postfix) with ESMTPSA id BB6801EF0A5
S:  for <[email protected]>; Thu, 11 Apr 2024 20:14:49 +0200 (CEST)
S: X-Is-Generated-Message-Id: true
S: MIME-Version: 1.0
S: Content-Transfer-Encoding: quoted-printable
S: Content-Type: text/plain;
S:  charset=UTF-8
S: Subject: <obfuscated>
S: From: Luuk <[email protected]>
S: Date: Thu, 9 Apr 2024 20:14:48 +0200
S: To: [email protected]
S: Message-ID: <[email protected]>
S: X-MailScanner-ID: BB6801EF0A5.A5150
S: X-MailScanner: Found to be clean
S: X-MailScanner-From: [email protected]
S: X-Spam-Status: No
S: 
S: 

• c#
• mailkit

Share Improve this question Follow edited Mar 9 at 15:32 Luuk asked Mar 9 at 13:49 LuukLuuk 15.1k55 gold badges2727 silver badges4444 bronze badges 8

• 1 The exception suggests that the IMAP server is dropping the connection. This can happen for a vast number of reasons ranging from a server crash, to throttling, to a mouse chewing through your ethernet cable. Since it sounds like this is on a local LAN that you are testing on, try getting the logs from the client and server and see if you can figure out what is going wrong. TO get client-side logs, change new ImapClient() to new ImapClient(new ProtocolLogger("imap.log")) (feel free to use a full path instead of just "imap.log"). Not sure how to get server logs for your server. – jstedfast Commented Mar 9 at 15:18
• Another option might be to use a program like Wireshark to get a TCP/IP log, but that's probably going to be more difficult for someone who has never done that before. – jstedfast Commented Mar 9 at 15:20
• FWIW, Thunderbird is getting the message list using something more like ImapFolder.Fetch(0, -1, MessageSummaryItems.UniqueId | MessageSummaryItems.Envelope) instead of downloading full messages just to build the message list. Later, when you click on a message, Thunderbird might be downloading the full message, but if it does, it is using the UID and not the message index. This might explain why Thunderbird works and your code does not. The server might have a bug when asking for a message by index instead of by UID. – jstedfast Commented Mar 9 at 15:26
• I added the new ProtocolLogger("imap.log"), and the output of the imap.log. Strange thing it that the content of the mail message is in the imap.log (It is s short message with only a SUBJECT) – Luuk Commented Mar 9 at 15:34
• Can you paste the last few (2-3) lines of the log? – jstedfast Commented Mar 9 at 15:36

 |  Show 3 more comments

1 Answer 1

Sorted by: Reset to default 1

Instead of downloading full messages to generate a "message list", use the following code:

public static void CheckIMAP()
{
    using (var client = new ImapClient())
    {
        client.Connect(mailserver, 143, SecureSocketOptions.None);

        client.Authenticate(username, password);

        IMailFolder folder = client.GetFolder("INBOX.subfolder");
        var fo = folder.Open(FolderAccess.ReadOnly);
        Console.WriteLine ("Total messages: {0}", folder.Count);
        var summaries = folder.Fetch(0, -1, MessageSummaryItems.Envelope | MessageSummaryItems.UniqueId);
        for (int i = 0; i < summaries.Count; i++)
        {
            try
            {
                Console.WriteLine("Message: {0}", summaries[i].Envelope.Subject);
            }
            catch (Exception ex)
            {
                System.Console.WriteLine($"MessageError {i}: {ex.Message}");
                break;
            }
        }
        System.Console.WriteLine();

        client.Disconnect(true);
    }
}

When you want to download the actual message, use summaries[i].UniqueId like this:

var message = folder.GetMessage(summaries[i].UniqueId);