Internet-Security.com TCP port 106 details

TCP port 106 is primarily used by the poppassd (POP Password Change) service/protocol for changing email account passwords.
Qualcomm Eudora’s “Change Password” feature used poppassd over TCP 106 to update mailbox passwords on compatible servers.
cPanel/WHM historically shipped a poppassd daemon (poppassd-cpanel) listening on 106 so mailbox users could change their passwords.
Mail systems including Dovecot (dovecot-poppassd), Courier (courierpassd/poppassd), and qmail setups with vpopmail have provided poppassd on this port.
Many ISPs and universities running POP/IMAP infrastructures (often with qpopper or similar) exposed a poppassd service on 106 for user password changes.
Security note: multiple poppassd implementations had past buffer-overflow and auth‑bypass flaws that were exploited for remote compromise, so this port has been targeted in scans/attacks.

TCP 106