macOS : Mail server connection issue with Mac Mail or Microsoft Outlook

By | March 14, 2025
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I recently faced recurrent and intermittent e-mail issue with macOS 15, where Mac Mail or Microsoft Outlook were in “disconnected mode”, unable to establish IMAP connection to fetch mail or SMTP connection to send mail.

NOTE : This example will assume that the remote mail service that we cannot connect from is “mail.itechlounge.net”.

Here are a few pointers to look at :

  1. Make sure the remote mail service is not experiencing any issue;
  2. Make sure your source IP is not blocked by the remote service (by repeated authentication failure for example);
  3. Try logging in to the Webmail to ensure your credentials works;
  4. Perform a DNS query (using dig, nslookup) to the mail service FQDN and ensure an address is returned;
  5. Try accessing the service from a different IP/location.

In my case, the issue was caused by a bug with the mDNSresponder that comes with macOS.  Randomly, I have been facing random DNS resolution issues that occurred intermittently.

Opening the “Terminal”, I found out that the DNS resolution for mail.itechlounge.net failed:

% telnet mail.itechlounge.net 993
mail.itechlounge.net: nodename nor servname provided, or not known

Using telnet for such test is an old habbit (and isn’t shipped by default with macOS anymore), NetCat is a great tool that does just that as well:

nc -zv mail.itechlounge.net 993

However the same query toward the DNS servers hosting the zone or toward any public DNS resolvers (such as 1.1.1.1, 8.8.8.8, 8.8.4.4, etc.) returned the proper destination address without any issue.

That narrow down the issue to be related to the macOS DNS caching service, which is handled by “mDNSresponder”.

Restarting mDNSresponder fixed the issue in my case :

sudo killall -HUP mDNSResponder

You should now be able to get working resolution on the mail FQDN :

user@hostname ~ % telnet mail.itechlounge.net 993
Trying 1.2.3.4...
Connected to mail.itechlounge.net.
Escape character is '^]'.
^]

The solution above worked for me, but is not a permanent fix, as the underlaying bug issue does not seem to have been fully addressed by Apple update releases. This is only a workaround to restore mail client connectivity until fully addressed by updates/fix.  The issue seem to be less present since macOS v15.3.