Welcome to the forums,
Code:
su zimbra
zmprov ms server.domain.com zimbraMailPort 81
zmcontrol stop
zmcontrol start
If you're using thick-clients, afterwards you may need to set:
Code:
zmprov ms server.domain.com zimbraMtaAuthHost server.domain.com
BTW are you aware of the modes?
CLI zmtlsctl to set Web Server Mode - Zimbra :: Wiki
If you run zmtlsctl then you will definately need to fix that zimbraMtaAuthHost (
SMTP Auth Problems - Zimbra :: Wiki)
Also, to change the HTTPS port it's zimbraMailSSLPort