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.