Which port does SMTP use by default? seenagape 11 years ago Which port does SMTP use by default? A.TCP port 21 B.TCP port 25 C.UDP port 25 D.UDP port 21 Explanation:SMTP uses TCP port 25.Incorrect Answers:A: TCP port 21 is used for FTP.C: SMTP uses TCP.D: Port 21 is for FTP, but is TCP, not UDP. ← Previous question Next question →