would spamfilters kill an unknown file format?

June 22, 2010 3:08 AM

would spamfilters kill an unknown file format?

I'm working on a project for which I'd like to establish a new file format. but since the files would have to be sendable much like a .pdf I'm concerned as to how spamfilters would react if a new and at least to them unknown file format would appear attached to an email. do most corporate email servers filter such messages as potential junk or virus-laden just because they don't know them or would this go through? how do the various webmailers react to unknown files being sent?

posted by krautland to computers & internet (5 answers total)

Make your new file format use XML, that won't trip them up. ZIP it to save space. In fact, this is what many of the newer file formats actually are.

OpenDocument and Office Open XML

(Whether or not XML is an appropriate way for you to actually store the data is a whole other story for which we would need more information than you've provided.)
posted by Brian Puccio at 3:29 AM on June 22, 2010

If you want to check you could try running it by ClamAV or virustotal but I doubt that it would trigger unless your file happened to contain a bytestring signature of known malware, which is astronomically unlikely. IMO no sane mail system would reject a message just because an attachment uses an unknown MIME-type, file extension, or file content, unless the admin has set it up as a whitelist to only allow certain known types. There however could indeed be non-sane mail systems out there but I wouldn't let it dictate your plans.
posted by Rhomboid at 3:39 AM on June 22, 2010

At my work we've never had any trouble with our custom formats. I've only ever seen spam filters block executables; I can't recall ever having trouble with any other format. I think you'll probably be fine.

But, yeah, make sure you're not reinventing the wheel. XML would be safest, if possible.
posted by equalpants at 3:43 AM on June 22, 2010

I work for a company that makes web and email content filtering software. Our software tries to identify as many types of files as possible, anything not recognised is flagged as "Unknown Binary" - many of our customers do block such files. Most services aimed purely at spam will not care however.
posted by AndrewStephens at 4:01 AM on June 22, 2010

thanks for your replies, guys. it's essentially a pdf with changed capabilities, so not executable. will ask about xml.
posted by krautland at 1:44 PM on June 22, 2010