Email with multiple recipients do not receive message


The following log extract is an example of when an email destined to multiple recipients gets dropped by the remote server when the first recipient fails, which prevents subsequent recipients from receiving the message even though they are valid.

Example log extract:

12/21/06 12:13:28 SMTP-OU  53FAF6AB46604BC89D3FFE9EB4D9835A.MAI 1016 MAIL 

MAIL FROM: <> SIZE=5607777 250 ok 48  8

12/21/06 12:13:28 SMTP-OU 53FAF6AB46604BC89D3FFE9EB4D9835A.MAI 1016 RCPT

RCPT TO:<> 554 Sorry, no mailbox here by that name. (#5.1.1) 30 51

12/21/06 12:13:28 SMTP-OU 53FAF6AB46604BC89D3FFE9EB4D9835A.MAI 1016 RCPT

RCPT TO:<> - 27 0

12/21/06 12:13:28 SMTP-OU 53FAF6AB46604BC89D3FFE9EB4D9835A.MAI 1016 QUIT

QUIT - 6 0


When MailEnable sends the same message to more than one recipient, it will try to send one message in the one connection to a remote server if the recipients have the same domain. This is to reduce bandwidth and improve performance. Some remote servers only accept a limited number of recipients for one message (to help reduce spam), or might drop the connection if one of the recipients is invalid. This can cause a bounce message to the sender indicating it failed to all recipients and the original message to not be delivered.


The following registry key allows the control of the maximum number of recipients allowed per outgoing message per domain. If the number of recipients is over this number, then the SMTP service will duplicate the message in order to send:

HKEY_LOCAL_MACHINE\SOFTWARE\Mail Enable\Mail Enable\Connectors\SMTP

The registry value is a DWORD and called: Maximum Recipients Per Domain

Setting the above key value to "1" which will create 1 message per recipient.

Restart the SMTP connector for the changes to take effect.

Product:MailEnable (All Versions)
Class:PRB: Product Problem or Issue
Revised:Wednesday, May 4, 2016