Firewall problems with Exchange Server 2007 email attachments

Microsoft Exchange Server 2007 may experience problems sending email attachments with file names over 50 characters in length when communicating through certain firewalls. Dušan Košarić,

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a Slovenian Exchange Server guru, recently posted about this peculiar issue on his blog.

The details seem odd: When sending email messages with attachments through certain types of firewalls, Exchange 2007 would sometimes report the error: 5.5.2 Invalid data in message. 

The type of email attachment doesn't seem to matter. The culprit is actually the name of the attachment: file names longer than 50 characters are rejected.

I conferred with Dušan on this issue, and he cited an older version of Symantec's Enterprise Firewall product as being one firewall that produces this problem.

Relates resources on Exchange 2007 and firewall interoperability:

Creating an ethical firewall in Exchange Server 2007

Beware of firewalls that block Exchange Server's SMTP/POP3 communications

Firewall policies and SMTP line lengths

Exchange Server 2007 Reference Center

In his words: "I got their firewall error details when this kind of email arrived and we found out there is a problem with CONTENT-DISPOSITION length, which is part of the header that contains attachment information. I must admit that I am still researching why this is happening, because it seems it happens only to email sent from Exchange 2007."

I may be totally off the mark, but my guess is that Exchange 2007 made changes to the way the Content-Disposition header is enumerated. Since this only seems to be happening rarely, I would guess they implemented it a little more rigidly. In turn, this might be causing problems for older firewalls that don't implement the Content-Disposition header quite as scrupulously.

In the meantime, the fix seems simple enough: upgrade the offending firewall. Failing that, make sure that people know not to send email attachments with overly long file names.

About the author: Serdar Yegulalp is editor of Windows Insight, a newsletter devoted to hints, tips, tricks, news and goodies for all flavors of Windows users.

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This was first published in July 2007

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