I have a ticket on Microsoft about my Symantec SMG (anti-spam) is receiving the "451 4.7.500 server busy" from mail.protection.outlook.co
m (Hybrid exchange 2010 / Office365 -and Postfix for some days) when I try to send a email to @hotmail.com (my send connector send to SMG. It has to be this way, and it was working until two days ago).
This question is the same point:
The Accepted Solution is:
"We were being throttled by Outlook.com addresses. Exchange was trying to send the health check emails outside. Fixed that and now everything goes through fine."
what does "Exchange was trying to send the health check emails outside. Fixed that and now everything goes through fine" mean?