Generally it depends on what services are running on the server.
All the ports which can be used by Parallels Plesk Panel/services are listed below:
#20 ftp-data (TCP) #21 ftp (TCP) #22 ssh (TCP) #25 smtp (TCP) #53 dns (TCP and UDP) #80 http (web server and Plesk updater) (TCP) #106 poppassd (for localhost only) (TCP) #110 pop3 (TCP) #113 auth (TCP) #143 imap (TCP) #443 https (TCP) #465 smtps (TCP) #587 mail message submission (TCP) #990 ftps (TCP) #993 imaps (TCP) #995 pop3s (TCP) #3306 mysql (TCP) #5224 (outgoing connections only) plesk-license-update (TCP) #5432 postgres (TCP) #8443 plesk-https (TCP) #8447 autoinstaller (TCP) #8880 plesk-http (TCP) #9080 tomcat (TCP)
Added since version 9.0:
#11443 sw-cp-serverd (TCP) #11444 sw-cp-serverd (TCP)
These two ports are used for SSO service when Billing is installed.
Additional Information
NOTE: none of these services should be denied access in /etc/hosts.deny and if /etc/hosts.deny includes some general access rules, then explicit allowing rules should be put in in /etc/hosts.allow for all ports mentioned (only ports that accept incoming connections).
