srl
SMTP
The Simple Mail Transfer Protocol (SMTP) sends email; IMAP or POP3 retrieve it. SMTP is the front door for phishing, spoofing, and BEC — and it is the protocol most often left at defaults on appliances, printers, and legacy applications.
Default ports:
Port Service Encryption 25 SMTP (MTA-to-MTA) Opportunistic STARTTLS 587 Submission (client-to-MTA) STARTTLS required 465 SMTPS Implicit TLS 2525 Alternate submission Varies UDP/25 is not a usable mail transport. Do not scan SMTP over UDP.