Attachments being modified in transit

Posted on 2014-03-18
Last Modified: 2016-06-02

I am somewhat perplexed by the following problem.

Our organization uses an Exchange 2010 server and Outlook 2010 clients.  The server itself was recently installed but we have been using Outlook 2010 for quite some time now.

For some strange reason attachments file types are being modified and I am unable to figure where the problem lies.

Here is a typical situation:

User1 and his assistant both communicate with the same client on a regular basis.  The client sends a message to user1 with a pdf attachment but it is received as an ATT00001.bin file.  The same client sends the exact same attachment to the assistant and she receives the .pdf file with no problems.

Logically if it was my server both users would either get the attachment unchanged or changed but not as mentioned above.

I am thinking that maybe the sender has a config problem but this problem has become more frequent recently and is affecting more users.  I suspect something in my environment but I am quite stumped.

Could it be my Watchguard XTM or maybe a configuration problem I haven't yet spotted on my Exchange server...

Anyone out there have any ideas?

Thank you in advance for your help.
Question by:Jay-P_C
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LVL 34

Expert Comment

by:Paul MacDonald
ID: 39936920
Is it possible User1 is accessing his e-mail using POP or IMAP rather than the native Exchange protocols?

Author Comment

ID: 39936989
I will have to check that...

What I do know right now that user1 received the mail in a PlainText format whereas his assistant received it in HTML format.

Hope this info is useful.
LVL 14

Expert Comment

by:Andy M
ID: 39937155
I'm not 100% sure but I believe if a HTML message with attachment is cnverted to plain text it can casue issues with the attachment. I would look into why he is getting it in plain-text format - possibly a client issue with Outlook?

What happens if the assistant forwards the email to the other user? Does the same problem occur or does the user recieve the email with attchement correctly? Does it still have the same issue in webmail?
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Author Comment

ID: 39937201
When user1's assistant forwarded the message to him it was fine attachment was in pdf format.

I also checked with his OWA and the message from his client was again in plaintext and the attachment was in .bin format.
LVL 63

Expert Comment

by:Simon Butler (Sembee)
ID: 39937286
That is classic interference. Does the Watchguard have any SMTP scanning functionality on it? If so then I would disable it if possible.

Is it only PDF files that have the problem? It could be how the other side is creating the PDF file which is causing problems for the scanner and it is unable to put them back as a PDF attachment when done scanning.

LVL 34

Expert Comment

by:Paul MacDonald
ID: 39937302
There is an issue with Exchange (at least with some versions) that would cause this problem.  It doesn't explain why only some of your users see it, unless they're connecting to different servers.

Author Comment

ID: 39937382
Simon, Paul,

The file "conversion" is not limited to pdf extension, it has also affected doc, docx and other commonly used filetypes.

What puzzles me is that the same sender wil send the exact same attachment to two people here and for the first person the attachment is usable whereas the second person is unable to open the file.

I would think that the smtp filtering on my firewall would give the same result to both users.

I will remove the Kaspersky antivirus from the problem user's machine to see if that is what is interfering.

I wil test further after everybody gets back from lunch... it's 12:36 here.

Thank you for your input, I really appreciate it.
LVL 14

Expert Comment

by:Andy M
ID: 39942164
Some other tests you can try which may help in narrowing down the issue:

1. Try sending attachment from another external address ( a google mail, yahoo address maybe) and see if that comes through converted to plain text with attachment garbled.

2. If this is the case, close outlook on client's machine, send attachment email again and look at it in OWA. If it's still got the same issue it's unlikley to be an issue on the client machine (as the email never even reached it).

3. Does the message header show it's been converted at all or have anything in it which may be relevant?

Accepted Solution

Jay-P_C earned 0 total points
ID: 39942752

I think I finally figured out the problem.  It turns out that the senders emails were using TNEF format for some of our adresses and HTML for the others.

The HTML emails were being received without any problems but the others were being stripped.

I added the TNEF format to the allowed content types in my smtp checking and am now awaiting further test results from my users and their clients.

To be continued...

Author Comment

ID: 39943454
It turns out that the quickest solution was to ask the sending party to delete the contact info from the email client and then just resend the message with attachments to the adressee using a manually entered email address.  The whole thing worked just fine.

Should have started with that but before "accusing" our client's email system my user insisted on me scouring through my email system...

Bottom line? Several hours wasted.

Thank you all for your input.

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