Hello Team, I installed our Ubuntu 22.04 server and placed Automated install on top of it: https://www.howtoforge.com/ispconfig-autoinstall-debian-ubuntu/ Unfortunately in Thunderbird it gets stuck on "Sending message" for really long time (like a minute or two), it's not a networking issue as when I send out emails via our other servers running older Ubuntu 20.04 server and "Automated install" and the slow outgoing email issue is not there. Receiving emails works fine, server load is really close to 0, server has 2 CPUs, 4GB RAM and 4 GB swap, swap is basically never used (looking at htop). I didn't do any customization to it except disabling IPv6 (both on client as well as server). I feel like there is some sort of timeout in place before the email is sent. Any ideas how to debug and later solve this? Thank you very much in advance.
Open shell window to your email-server, issue command Code: tail -f /var/log/mail.log Keep that window open while sending test e-mail. In Thunderbird, when sending the test e-mail, turn on the getting report of delivery setting. It is in one of the drop down menus at top of writing message -window.
Thank you @Taleman I'll keep an eye on it unfortunately for now it seems that the problems went away so I won't be able to debug it. I also noticed tons of bans in log of fail2ban (like really insane amount of bans on level of fraction a second) and also some emails start arriving twice (from 3rd parties) or even more than twice (the exact same email). Maybe it's related to the attack? Edit: I'm starting to think it's related to this: https://forum.howtoforge.com/threads/fail2ban-to-slow-need-delay-for-login.90421/
It is quiet possible that bruteforce attack can lead to such behaviour. This would explain why the sending of the email takes so long, the client trys logging in for a long time while the server is busy answering all the login attempts.
