Since yesterday my Postfix stopped working: It doesn't receive any e-mails anymore (from other email addresses, not my own). There's nothing in mail.log or mail.err. Yesterday I installed fail2ban on my Ubuntu, did update & upgrade, and installed sendmail with fail2ban, which was an error, I removed sendmail again. But now I just can't get postfix to work. When I get its status it says
root@vps219158:/etc/init.d# sudo systemctl status postfix.service * postfix.service Loaded: masked (/dev/null; bad) Active: inactive (dead)
And when I try to restart it
Failed to restart postfix.service: Unit postfix.service is masked.
I don't understand why it is masked.
Fail2ban is deactivated, I also checked the iptables: Nothing is banned. When I send an email to my email account from any one of my 3 other email accounts (@hotmail.com etc.) it doesn't report that the mails couldn't be sent - they just don't appear in my inbox (i.e. not on the server, "mail" command shows no new mails).
What more could I test? What could possibly lead to this issue?
EDIT: Status is: From outside, the SMTP connection fails. Postfix says it's running. Nothing in mail.log/err. It ran until yesterday. On localhost, I can telnet to "localhost 25" and send a mail, but it doesn't get to my inbox (same for ehlo mydomain.com and ehlo localhost).
Thanks in advance for some help!