Attachment are being removed from outbound emails

Hello MS team,

I have a client who is running into some email issues:

Issue description:

Company developed an application server that basically uses a CRM tool and send bulk emails using a shared mailbox that is hosted on a Exchange 2013 server.

This application has been working well for a while, but suddenly they are receiving complains that all emails sent from that application do not contains attachments, somehow all attachments are being deleted.

I did a message tracking, and was able to see attached screenshots

What could be happened that emails flow OK, but attachments are being removed?

Exchange infrastructure:

Exchange 2013 SP1, multiple CAS behind a F5, multiple MBX servers in a DAG, multiple DC, GCs, WIndows 2008 R2 forest and domain level, The OS in Windows 2012 R2 standard edition on all exchange VMs, Outlook version is 2013

According to application team, no changes made to application servers.

by the way, because the application uses a shared mailbox, the AD account for this mailbox is disabled in AD, I guess this is expected because is a shared mailbox? is that assumption correct?
Jerry SeinfieldAsked:
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Check whether the attachment restriction/removal is part of the outgoing policy set on the exchange.  The issue might also be that the encoding of the attachment is such that it is not displayed/handled on the receiving end.

Send your self, a message internally as well to an external email address.
Jerry SeinfieldAuthor Commented:
Hi Arnold

Thanks for the quick response

Can you please provide me your thoughts in regards to the 2 screenshots attached? can you confirm the messages were or not sent?
The trace has events that are/have meaning but I am not in a position to determine which hadiscard, ha redirect, etc.
Check whether you have a routing policy restriction transmission of attachments.

Check the hypothesis, mail to an internal email address and to an external address.

The attachment restriction might be content based.

Looking at the trace where redacted everything without a reference which if the entries apply to the same message, versus other.  Looked at the times and could not make out whether they are sequential or one dealt what was coming and the other having met the rule was going out.

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Jerry SeinfieldAuthor Commented:
we do not have any routing policy transmissions of attachment or any transport rules
Jerry SeinfieldAuthor Commented:
at the end of day, the shared mailbox reached its own mailbox size quota, therefore unable to send attachaments and external emails
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