ZCS Administrator Guide 8.0
ZCS Administrator Guide 8.0
Network Edition

Zimbra Mail Transfer Agent > SMTP Authentication

SMTP Authentication
SMTP authentication allows authorized mail clients from external networks to relay messages through the Zimbra MTA. The user ID and password is sent to the MTA when the SMTP client sends mail so that the MTA can verify if the user is allowed to relay mail.
User authentication is provided through the Zimbra LDAP directory server, or if implemented, through the Microsoft Active Directory Sever.
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