IMAP connecting not working on Windows, does on mobile and MAC

PieterVH

• November 07, 2022 07:44

Hi There, My old server got corrupted after a restart (all was working before), so I took a new dedicated server to move all my 96 accounts. Server managers dit that for me. So far all good. Now people with windows computers start complaining the mail can't connect (tried with Thunderbird, and Outlook) with their mail accounts. Mac mail: connects within a second Outlook Mac: connects within a second Outlook iPhone: connects within a second. Webmail: works like a charm. DNS records are good (e-mail deliverabillity tab gives a checkmark) I restarted IMAP server and mailing server several times. My server guys say nothing is odd and it can't be something in the new WHM configuration. I thought of IP bans, but the logs are clean. Is there anyone who has a clue of what might be happening here?

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  kodeslogic

  • November 07, 2022 13:42

  Try to change the incoming server settings as below: Port: 993 or 143 Connection Security: Auto
  

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  cPRex Jurassic Moderator

  • November 07, 2022 14:28

  You could also try disabling the firewall temporarily on the new machine to see if that is related to the issue.

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  ITHKBO

  • November 08, 2022 12:14

  It sounds like it might be a issue related to TLS protocol versions active on the Windows clients *if the firewall and cPHulk Bruteforce Protection is not showing anything*. Can you crosscheck what TLS and ciphers are allowed on the server in EXIM and one of the problematic clients? Exim Configuration Manager-> Basic Editor -> Security -> Options for Open SSL Should read something like this: +no_sslv2 +no_sslv3 +no_tlsv1 +no_tlsv1_1
  To check on Windows we use IIS Crypto as powershell is a pain with this kind of audit. We have had past cases with Windows Message User Agents (MUA's) trying the connection with a lower version than allowed by our servers causing connection issues without a clear error in MUA. This in turn required us to monitor live port access on the mail server. After some time we found out some Windows clients used TLS1.0 or 1.1 to connect which are considered End of Life (EOL) disabling the protocols on the Windows client with a restart solved that issue. Be sure to verify that no legacy software still requires any EOL protocol before disabling its functionality.

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  martin MHC

  • December 09, 2022 14:23

  We have a very similar issue this morning; it appears that a MS Outlook update (I assume) has caused Outlook to somehow mess up displaying data to the customer. We have logs on the server that emails are received by the mailbox and that Outlook connects ok to the server, but Outlook internally doesn't display these emails to the client.

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