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One of the mail server clients is running into issues with secured SSL IMAP connections ( he has to use a multiple email accounts on the same computer).
I was informed that part of the email addresses are working correctly, however the newly created ones were failing to authenticate even though all the Outlook Express email configuration was correct as well as the username and password typed in were a real existing credentials on the vpopmail server.
Initially I thought, something is wrong with his newly configured emails but it seems all the settings were perfectly correct!
After a lot of wondering what might be wrong I was dumb enough not to check my imap log files.
After checking in my /var/log/mail.log which is the default log file I’ve configured for vpopmail and some of my qmail server services, I found the following error repeating again and again:
imapd-ssl: Maximum connection limit reached for ::ffff:xxx.xxx.xxx.xxx" imapd-ssl error
where xxx.xxx.xxx.xxx was the email user computer IP address.
This issues was caused by one of my configuration settings in the imapd-ssl and imap config file:
In /usr/lib/courier-imap/etc/imapd there is a config segment called
Maximum number of connections to accept from the same IP address
Right below this commented text is the variable:
As you can see it seems I used some very low value for the maximum number of connections from one and the same IP address.
I suppose my logic to set such a low value was my desire to protect the IMAP server from Denial of Service attacks, however 4 is really too low and causes problem, thus to solve the mail connection issues for the user I raised the MAXPERIP value to 50:
Now to force the new imapd and imapd-ssl services to reload it’s config I did a restart of the courier-imap, like so:
debian:~# /etc/init.d/courier-imap restart
That’s all now the error is gone and the client could easily configure up to 50 mailbox accounts on his PC 🙂