About 6 months ago, I have bought a VPS from Aruba, to use as a web and mail server for my projects. I have installed ISP Config following this tutorial https://www.howtoforge.com/tutorial...-stretch-apache-bind-dovecot-ispconfig-3-1/3/. I use web server, ftp server and database server without problem, but the only flaw is the mail server. It's usually unreachable from mail client such as Mail (WIN10) or Thunderbird: it stays about five minutes trying to donwload messages, and at the end it fails with timeout. Domains which point to VPS are mrtsolutions.it and tech.croceverdeponte.it (last only mail server). About 1 time of 3 it's all ok and I can do everything without waiting. For example on Mail (WIN10) I have 2 outgoing email from ***@tech.croceverdeponte.it and after 20 minutes they're always in "outgoing" section. Sometimes it gives me "error in login into this account", it let me change the password and that's all ok, i can send/receive email. After 10 minutes same errors again. Can you help me?