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Unable to send email with TIF/TIFF attachments

I am unable to send emails with TIF/TIFF files attached outside our organisation.  Emailing them internally works fine, so my suspicions are with the ClearSwift MailSweeper for SMTP.  The following is logged in the event log

EventID 792
Network I/O error 10054 (0x00002746) encountered when sending message data to <mailserver>

I also receive regular emails stating that the email is delayed (see below);

Your message has been delayed and is still awaiting delivery to the following recipient(s):

user@domain.com
Message delayed


I/O error encountered
during command: (message data)

Any help greatly appreciated.
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JonathanCoupland
Asked:
JonathanCoupland
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2 Solutions
 
moorhouselondonCommented:
TIF extensions should pass through without problem.  Try renaming the file without an extension to test whether that works.

What I would look at though is the size of these attachments.  TIF files can be pretty enormous in size.
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JonathanCouplandAuthor Commented:
The TIF file(s) are only around 120k.  I have tried renaming them, but the problem still persists.
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moorhouselondonCommented:
The wikipedia entry for TIFF does have this to say, which might be the cause of blocking:-

http://en.wikipedia.org/wiki/TIFF

Exploits
The TIFF file format is unusual in comparison to other image formats, in that it is composed of small descriptor blocks containing offsets into the file which point to the actual pixel image data (composed of bands of pixel rows). This means that incorrect offset values can cause programs to attempt to read erroneous portions of the file or attempt to read past the physical end of file. Like most other image file formats, improperly encoded packet or line lengths within the file can cause poorly written rendering programs to overflow their internal buffers. Properly-written image rendering programs generally avoid such pitfalls.
Multiple buffer overflows have been found in Libtiff.[1][2][3] Some of these have also been used to execute unsigned code on the PlayStation Portable,[4] as well as run third party applications on the iPhone and iPod Touch[citation needed].
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moorhouselondonCommented:
These mailsweeper "appliances" do seem to cause a lot of problems.  From the fact that you renamed the file and problem persists, it sounds like the mailsweeper thing is not parsing the outgoing mail stream correctly.  Have you tried zipping it?  
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JonathanCouplandAuthor Commented:
The issue is now resolved.  I was able to zip the file and it would then get delivered to the recipient.  It turns out that it was getting blocked by one of our 'Intrusion Dectection' systems!  Many thanks for the advice
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