Hi,
I am having problem at times with 1 of my messaging gateway, though the email address exists in Protocols> SMTP> Domains the sender gets a delivery failure
Delivery has failed to these recipients or distribution lists:
concerned email address
Your message wasn't delivered because of security policies. Microsoft Exchange will not try to redeliver this message for you. Please provide the following diagnostic text to your system administrator.
The following organization rejected your message: AntiSpam (name of the messaging gateway).
AntiSpam #550 5.7.1 < email address >... email address ... No such user ##
I had same problem on 11/11/16, I then whitelisted the sender domain. Today I have whitelisted the connection IP. Strange thing is that when I check on messaging gateway log, I do not find anything.
Can you please help for me to troubleshoot this problem. As already mentioned it happens on and off. Last time was 11/11/16, then it happened today also. Thanks to help!! What could be causing such an issue