Internet-Security.com TCP port 3310 details

TCP port 3310 is primarily used by ClamAV’s clamd daemon, the network file-scanning service.
Mail transfer agents integrate with clamd over 3310, e.g., Exim’s malware/clamd scanner and Postfix via Amavis or MailScanner configured to 127.0.0.1:3310.
Rspamd’s antivirus module uses ClamAV on 3310 by default in many deployments.
Nextcloud’s Files Antivirus app can connect to clamd on TCP 3310 to scan uploads.
The Haraka SMTP server’s clamav plugin defaults to 127.0.0.1:3310.
Containerized mail stacks like Mailu and docker-mailserver run a clamd service listening on 3310 (internally) for other components.

TCP 3310