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NDR QUESTION - exchange 2010

I am trying to understand the NDR messages setup beforehand by someone else.

I sent 2 test emails from outside the organization, above the set limit for attachments.
The limit is set to 11MB.

I sent a 13MB email and got a NDR from - Mail Delivery System title 'Undelivered Mail Returned to Sender'
I sent a 12MB email and got a NDR from - Postmaster@xxx.com title 'Undeliverable: subjectname'

Can someone explain where the emails are coming from, and how the system is differentiating between the 2 different emails?  Basically, how come one email is from postmaster and other is from mail delivery system.

We would like the postmaster message as it looks better and has explanation.
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1 Solution
Simon Butler (Sembee)ConsultantCommented:
You need to check all of your limits, because I would expect the same NDR to be returned. I suspect that one of the limits is different. Check Send and Receive Connectors, global settings and also anything else that touches email, such as firewalls, AV software etc.

With a 11mb limit, a 12mb and 13mb file could be handled differently, because the limit is not equal. A 12mb attachment could be 18mb or more as seen by Exchange because of encoding overhead. It depends on the attachment type.

drmpAuthor Commented:
Should all connectors/global settings be set to the same?
Im guessing yes for our environment but  wanted to ask
Simon Butler (Sembee)ConsultantCommented:
Yes, the best practise is to have everything the same.
If you want then limit certain traffic types, use transport rules.

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