During a random check of my postfix logs (which always leave me worried when I see all those attempts to use my server as a relay) I noticed lines like these:
Jul 01 01:26:37 *** postfix/smtpd: connect from unknown[XX.XX.XX.XX] Jul 01 01:26:37 *** postfix/smtpd: lost connection after UNKNOWN from unknown[XX.XX.XX.XX]
Each second, three of these requests were made, in total 72 last night. Since November last year, a total of 1198 of such requests exist in the server logs. Although not particularly many, what worries me is that I can't find anything related via google. Apparently, somebody tries a command that postfix doesn't know.
Is this kind of attack known? Can I do anything against it? Thank you!