[TriLUG] OT: mail servers corrupting our attachments

[Craig Duncan]

Christopher L Merrill wrote:

> I guess this is OT, since OUR servers (BSD and Linux) do NOT have this
> problem.  We send out license keys to our customers via email.  The keys
> are encrypted files (i.e. binary).  We've always received reports of the
> license keys arriving corrupted.  But the reports are becoming more and
> more frequent.  When we zip the key and resend it (manually), the keys
> always get through.
>
> Firstly, I don't understand why the servers are corrupting any 
> attachments.
> I could understand if they were simply stripped...by malware filters, for
> instance.
>
> I surmise that if the servers were actually inspecting the contents of
> the files, both look like binary files, so both should get munged.  But
> since only the non-.zip files get munged, the servers are looking at
> either the first few bytes to identify Zip files (PK...) or they are
> looking at the file extensions.  Since I've heard people recommend
> renaming files to *.zip to get past mail filters, I suspect that some
> or all of these servers are looking at file extensions.
>
>
> So finally...my questions:
>
> Is it common for mail servers or malware scanners to use the filename
> extension to determine the attachment type?
>
> If we simply renamed our licence keys to *.zip, would we cut down the
> frequency of our corrupted key compaints?
>
> Any other suggestions?
>
>
> TIA,
> C
>
>
>
In addition to sending the binary file you could also send the md5 hash  
so that your customers can verify the integrity of the file and help you 
identify where the issue really lies.