I'm troubleshooting an issue with a particular sender sending mass mailings to a distribution list in our company. They advise they are getting rejected because our mail server is not responding in a timely fashion. This is causing the mail to not get through on our primary MX, which tries our secondary MX, and ultimately fails (because our secondary mx is not accepting smtp purposely)
The sender is not getting an error from the primary MX, only the secondary because of the failure.
I am wondering though if there is some rate limiting that could be the issue here. I've confirmed through our anti-spam logs and whitelisted all sender IPS, but don't even see it reaching our Edge Server logs.
I'm wondering what is a way to troubleshoot to see if the message is not being delivered because of it reaching a certain limit on our Edge servers.
I've checked the Transport server settings, and they are the defaults, and i've reviewed the event log for any MSExchangeTransport events, and I don't see any 1021 or 1009 events.
Are there any other event numbers I should be reviewing or some way see the SMTP traffic and hopefully capture why the edge server is rejecting the traffic?
Also is there a way to see the current/active or historical inbound connections, so I can gauge whether our limits are close to being reached. We are a large organization with heavy mail flow, so I wouldn't be surprised if this is necessary, I'd just like to see where we are now.
Thanks in advance.