Postfix possible SMTP attack and blacklist - email

Question

I have plesk 12.5.30 on my server which is often blacklisted on Symantec Mail Security reputation.
The ip is new (I have purchased the server on 13.02.2017).
Also my ip is blacklisted on BACKSCATTERER.
Seeing the log of postfix I have a lot of entries like
Mar 22 14:51:43 server postfix/smtpd[14204]: connect from 75-143-80-240.dhcp.aubn.al.charter.com[75.143.80.240]
Mar 22 14:51:45 server postfix/smtpd[14204]: lost connection after EHLO from 75-143-80-240.dhcp.aubn.al.charter.com[75.143.80.240]
Mar 22 14:51:45 server postfix/smtpd[14204]: disconnect from 75-143-80-240.dhcp.aubn.al.charter.com[75.143.80.240]
Mar 22 14:51:50 server postfix/smtpd[14204]: connect from 128.128.72.76.cable.dhcp.goeaston.net[76.72.128.128]
Mar 22 14:51:51 server postfix/smtpd[14204]: lost connection after EHLO from 128.128.72.76.cable.dhcp.goeaston.net[76.72.128.128]
Mar 22 14:51:51 server postfix/smtpd[14204]: disconnect from 128.128.72.76.cable.dhcp.goeaston.net[76.72.128.128]
Mar 22 14:52:19 server postfix/smtpd[14204]: connect from mail.dedeckeraccountants.be[91.183.46.186]
Mar 22 14:52:19 server postfix/smtpd[14204]: disconnect from mail.dedeckeraccountants.be[91.183.46.186]
I have
Changed the smtp port to a non standard one (9456)
Installed firewall and fail2ban on plesk and setted as in image
Setted mail settings of plesk as in image
Installed a spamassasin
I have noticed also that some days ago i have lines in log like these
Mar 19 06:47:00 server postfix/smtp[13517]: CCC1C510023D: to=<229e7dc3183452c7d3290d1ba28f073e#www.lablue.de>, relay=none, delay=235637, delays=235636/0.05/0.09/0, dsn=4.4.1, status=deferred (connect to www.lablue.de[217.22.195.26]:25: Connection refused)
Mar 19 06:47:00 server postfix/smtp[13503]: 7EDD55100138: to=<Weber226#brockel.kirche-rotenburg.de>, relay=kirche-rotenburg-verden.de[136.243.213.122]:25, delay=239980, delays=239979/0.01/0.35/0.1, dsn=4.0.0, status=deferred (host kirche-rotenburg-verden.de[136.243.213.122] said: 451 Temporary local problem - please try later (in reply to RCPT TO command))
Mar 19 06:47:00 server postfix/smtp[13504]: 97B055100233: to=<office#angerlehner.at>, relay=none, delay=222922, delays=222922/0.01/0.64/0, dsn=4.4.3, status=deferred (Host or domain name not found. Name service error for name=angerlehner.at type=MX: Host not found, try again)
Mar 19 06:47:00 server postfix/smtp[13509]: 1E15F510019B: host mx1.leventboru.com.tr[89.19.1.69] said: 450 4.7.1 Recipient address rejected: Requested action not taken: mailbox unavailable or not local (in reply to RCPT TO command)
And i noticed a very long mail queue in plesk settings (i have deleted all mail in queue)
Any advice to block this attack??
Thanks in advance
Edit: I want to share my plesk-postfix settings
[plesk-postfix]
enabled = true
filter = postfix-sasl
action = iptables-multiport[name="plesk-postfix", port="http,https,smtp,submission,pop3,pop3s,imap,imaps,sieve", protocol=tcp]
logpath = /var/log/maillog
maxretry = 2
There is somenthing can i improve here?

Answer 1

You might consider to use a Fail2Ban - filter with the following regex - expressions:
failregex = ^%(__prefix_line)slost connection after (AUTH|UNKNOWN|EHLO) from [^\[]*\[<HOST>\]\s*$
If you need further Fail2Ban regex - expressions, pls. consider to ADD the corresponding log - file entries, because some general standart ones may not suit your needs or/and your qmail/postfix/imap-courier/dovecot version, installed on your server. ;-)
Edit:
In order to be more precise, I now add the full suggestion, incl. the regex, that #MattiaDiGiuseppe already used in his comments - it's just a bit better formatted this way.
[Definition]
_daemon = postfix(-\w+)?/(?:submission/|smtps/)?smtp[ds]
failregex = ^%(__prefix_line)swarning: (.*?)does not resolve to address <HOST>: Name or service not known$
^%(__prefix_line)swarning: [-._\w]+\[<HOST>\]: SASL ((?i)LOGIN|PLAIN|(?:CRAM|DIGEST)-MD5) authentication failed(:[ A-Za-z0-9+/:]*={0,2})?\s*$
^%(__prefix_line)sNOQUEUE: reject: RCPT from \S+\[<HOST>\]: 554 5\.7\.1 .* Relay access denied.*$
^%(__prefix_line)sSSL_accept error from \S+\s*\[<HOST>\]: lost connection$
^%(__prefix_line)sSSL_accept error from \S+\s*\[<HOST>\]: -1$
^%(__prefix_line)slost connection after (AUTH|UNKNOWN|EHLO) from [^\[]*\[<HOST>\]\s*$
ignoreregex = authentication failed: Connection lost to authentication server$
Pls. consider to have a look at all standart filters ( for Fail2Ban 0.10 AND older versions), by visiting:
=> https://github.com/fail2ban/fail2ban/tree/0.10/config/filter.d
If you desire to view the standarts for older versions, just click on the "Branch: 0.10" dropdpwn - button, pls.