This is not working and Roundcube doesn't event show an error. It just get stuck working and finally a timeout (let me say firewall is disabled)....
I attached `mail.log` output when I try to use Thunderbird. (unmasked IPs are spammers.)
Thanks for sharing that useful link. However, I think almost provided the most information I had. I'm running ISPConfig 3.2.1 on Ubuntu 20.04....
I have set up an Ubuntu 18.04 server using Perfect server tutorial and it was working for almost 2 years without a problem. But SMTP stopped...
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