This article describes the capabilities and limitations of the setting called "Maximum number of recipients per message" in Messaging Gateway's (SMG) Advanced SMTP Settings.
By default, Symantec Messaging Gateway (SMG) allows a maximum of 1024 recipients per email message, regardless of it being inbound or outbound.
If needed, this setting can be changed to limit or increase the number of allowed recipients for a single email message.
To change the setting, browse to "Administration > Hosts > Configuration > SMTP > Advanced"
Pease note that this feature only applies to the Messaging Transfer Agents (MTA) or remote mail sending servers, that use separate "RCPT TO:" lines during the SMTP conversation with SMG.
In such communications, SMG will identify those RCPT TO: actions and once the limit is reached it will respond with the following message:
“452 4.5.3 Service unavailable, recipients per message limit reached.”
...for each remaining RCPT TO: action. After the RCPT TO: actions complete, the delivery will proceed eventually with the DATA verb and remaining transaction. The message will still attempt to be delivered to the initial recipients.
This functionality can be tested by setting the “Maximum number of recipients per message” to a very low number such as "3", then simulating an SMTP transaction with telnet.
Just provide several RCPT TO: actions until the limit is exceeded. More information on how to send a mail through a Telnet session is available in the following article: