==== Required information ====
- iRedMail version (check /etc/iredmail-release):
- Linux/BSD distribution name and version:
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):
- Web server (Apache or Nginx):
- Manage mail accounts with iRedAdmin-Pro?
- Related log if you're reporting an issue:
====

What does this mean?

Aug 20 18:24:05 mail02 postfix/smtpd[6270]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:05 mail02 postfix/smtpd[6270]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:05 mail02 postfix/smtpd[6124]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:05 mail02 postfix/smtpd[6124]: connect from unknown[155.133.18.81]
Aug 20 18:24:06 mail02 postfix/smtpd[6124]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:06 mail02 postfix/smtpd[6124]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:06 mail02 postfix/smtpd[6270]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:06 mail02 postfix/smtpd[6270]: connect from unknown[155.133.18.81]
Aug 20 18:24:06 mail02 postfix/smtpd[6270]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:06 mail02 postfix/smtpd[6270]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:06 mail02 postfix/smtpd[6124]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:06 mail02 postfix/smtpd[6124]: connect from unknown[155.133.18.81]
Aug 20 18:24:07 mail02 postfix/smtpd[6124]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:07 mail02 postfix/smtpd[6124]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:07 mail02 postfix/smtpd[6270]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:07 mail02 postfix/smtpd[6270]: connect from unknown[155.133.18.81]
Aug 20 18:24:07 mail02 postfix/smtpd[6270]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:07 mail02 postfix/smtpd[6270]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:07 mail02 postfix/smtpd[6124]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:07 mail02 postfix/smtpd[6124]: connect from unknown[155.133.18.81]
Aug 20 18:24:08 mail02 postfix/smtpd[6124]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:08 mail02 postfix/smtpd[6124]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:08 mail02 postfix/smtpd[6270]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:08 mail02 postfix/smtpd[6270]: connect from unknown[155.133.18.81]
Aug 20 18:24:08 mail02 postfix/smtpd[6270]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:08 mail02 postfix/smtpd[6270]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:08 mail02 postfix/smtpd[6124]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:08 mail02 postfix/smtpd[6124]: connect from unknown[155.133.18.81]
Aug 20 18:24:09 mail02 postfix/smtpd[6124]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:09 mail02 postfix/smtpd[6124]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:09 mail02 postfix/smtpd[6270]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:09 mail02 postfix/smtpd[6270]: connect from unknown[155.133.18.81]
Aug 20 18:24:09 mail02 postfix/smtpd[6270]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:09 mail02 postfix/smtpd[6270]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:09 mail02 postfix/smtpd[6124]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:09 mail02 postfix/smtpd[6124]: connect from unknown[155.133.18.81]
Aug 20 18:24:10 mail02 postfix/smtpd[6124]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:10 mail02 postfix/smtpd[6124]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:10 mail02 postfix/smtpd[6270]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:10 mail02 postfix/smtpd[6270]: connect from unknown[155.133.18.81]
Aug 20 18:24:10 mail02 postfix/smtpd[6270]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:10 mail02 postfix/smtpd[6270]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:10 mail02 postfix/smtpd[6124]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:10 mail02 postfix/smtpd[6124]: connect from unknown[155.133.18.81]
Aug 20 18:24:11 mail02 postfix/smtpd[6124]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:11 mail02 postfix/smtpd[6124]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:11 mail02 postfix/smtpd[6270]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:11 mail02 postfix/smtpd[6270]: connect from unknown[155.133.18.81]
Aug 20 18:24:11 mail02 postfix/smtpd[6270]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:11 mail02 postfix/smtpd[6270]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:11 mail02 postfix/smtpd[6124]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:11 mail02 postfix/smtpd[6124]: connect from unknown[155.133.18.81]
Aug 20 18:24:12 mail02 postfix/smtpd[6124]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:12 mail02 postfix/smtpd[6124]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:12 mail02 postfix/smtpd[6270]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:12 mail02 postfix/smtpd[6270]: connect from unknown[155.133.18.81]
Aug 20 18:24:12 mail02 postfix/smtpd[6270]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:12 mail02 postfix/smtpd[6270]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:12 mail02 postfix/smtpd[6124]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:12 mail02 postfix/smtpd[6124]: connect from unknown[155.133.18.81]
Aug 20 18:24:12 mail02 postfix/smtpd[6124]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:12 mail02 postfix/smtpd[6124]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:13 mail02 postfix/smtpd[6270]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:13 mail02 postfix/smtpd[6270]: connect from unknown[155.133.18.81]
Aug 20 18:24:13 mail02 postfix/smtpd[6270]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:13 mail02 postfix/smtpd[6270]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:13 mail02 postfix/smtpd[6124]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:13 mail02 postfix/smtpd[6124]: connect from unknown[155.133.18.81]
Aug 20 18:24:14 mail02 postfix/smtpd[6124]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:14 mail02 postfix/smtpd[6124]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:14 mail02 postfix/smtpd[6270]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:14 mail02 postfix/smtpd[6270]: connect from unknown[155.133.18.81]
Aug 20 18:24:14 mail02 postfix/smtpd[6270]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:14 mail02 postfix/smtpd[6270]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:15 mail02 postfix/smtpd[6124]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:15 mail02 postfix/smtpd[6124]: connect from unknown[155.133.18.81]
Aug 20 18:24:15 mail02 postfix/smtpd[6124]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:15 mail02 postfix/smtpd[6124]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:15 mail02 postfix/smtpd[6270]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:15 mail02 postfix/smtpd[6270]: connect from unknown[155.133.18.81]
Aug 20 18:24:15 mail02 postfix/smtpd[6270]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:15 mail02 postfix/smtpd[6270]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:16 mail02 postfix/smtpd[6124]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:16 mail02 postfix/smtpd[6124]: connect from unknown[155.133.18.81]
Aug 20 18:24:16 mail02 postfix/smtpd[6124]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:16 mail02 postfix/smtpd[6124]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:16 mail02 postfix/smtpd[6270]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:16 mail02 postfix/smtpd[6270]: connect from unknown[155.133.18.81]
Aug 20 18:24:16 mail02 postfix/smtpd[6270]: lost connection after AUTH from unknown[155.133.18.81]
Aug 20 18:24:16 mail02 postfix/smtpd[6270]: disconnect from unknown[155.133.18.81]
Aug 20 18:24:17 mail02 postfix/smtpd[6124]: warning: hostname ptr-155.133.18.81.vmline.pl does not resolve to address 155.133.18.81: Name or service not known
Aug 20 18:24:17 mail02 postfix/smtpd[6124]: connect from unknown[155.133.18.81]