Email NDR from external address - is this related to Exchange 2010 - 2016 migration

[MrLudwig]

Hi,

 

One of our staff users has received three email NDR's today when sending to three different external addresses. Normally I wouldn't think much of this, two or them were simple RecipientNotFound errors from the servers at the other end suggesting the email address is either wrong or no longer exists. The third was not one I'd seen before - Remote Server returned '550 5.4.1 [[email protected]]: Recipient address rejected: Access denied.

 

I've had a good look around the Interweb and most of the bits I found seem to suggest this might be a problem related to issues between an on-prem Exchange server and Exchange Online. This would be at the recipient end so nothing to do with us.

 

However, I am a little bit paranoid at the moment as I'm in the process of an Exchange 2010 to 2016 migration here, so anything email related has me on edge, so to speak.

 

Our migration seems fine and there doesn't appear to be any other problems, emails are flowing in and out and between 2010 and 2016 OK, so I'm almost sure this is a problem at the recipient end, but there is this little nagging voice of doubt in my head that isn't convinced just yet. Also, I will be looking at a move to a hybrid Office365 set up at some point in the future so any info that would help me avoid this same problem in future would be helpful too.

 

Thanks

[chaplic]

My educated guess is that it’s an address that only accepts internal emails (like a Distribution list), so their end, but being paranoid at this time is not a bad thing.

 

For extra assurance, double check your SPF record to ensure it’s valid and includes the 365 servers

[MrLudwig]

Thanks chaplic,

 

Feeling less paranoid now; our emails are still fine so pretty sure this was indeed something at the recipient end. A restricted account or distribution list would seem logical explanation too.

 

Thanks again.