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Journal millahtime's Journal: Hotmail filters sent emails to spam 6

hotmail (Microsofts webmail service) is filtering mail written in (a mac OS X) program directly to the junk mail folder and I figured out what they are doing.

It started when some mail that went out of a mail server I manage was incorrectly filtered by hotmail as junk email. In the interest of knowing what was going I performed several tests to obtain the details of the problem.

First, I tried sending from several other methods. This included sending from other mail programs in unix, webmail, etc. Some of these under the same routing path through my firewall. All of the other mail programs, whether by webmail or smtp, sent and were not filtered to junk. But, was consistantly filtered to junk.

So, I decided to try and fool hotmails filters so they would think it was coming from and see if I could find what they were filtering based on.

In the headers of the email there are two specific lines that tell you the email was generated by and apple product and specifically:

X-Mailer: Apple Mail (2.733)
MIME-Version: 1.0 (Apple Message framework v733)

At first I tried scripting, in PHP, scripts to send to a test email address and see what was identified as spam. Using mail(), which uses qmail on my setup, and sendmail itself in another setup caused the mail to not be filtered. Hotmail seems to realize mail is from these programs and not so it is not filtered.

Next, I tried scripting so that the email interacts directly with a known good smtp server. In my case I used comcasts mail server as they are my internet provider. I used a script already generated to do smtp that can be found here. When I added:

X-Mailer: Apple Mail (2.733)

to the header it is filtered to the junk folder in hotmail.

So, hotmail looks for this header and to make sure the email is not from sendmail or qmail. In these cases the email is filtered to the spam folder.

REAL NICE Microsoft.
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Hotmail filters sent emails to spam

Comments Filter:
  • Did you submit this as a main slashdot article? I never knew about this and I think other slashdoters would like to know (besides the ones that noticed the link in your sig).
  • I agree! Post it to slashdot as a main story. First you should post your documentation of the tests to a page that can handle the traffic.

    Alternatively you could also contact some tech news outfits and see if they can duplicate your results. If this is for real, then MS needs to be spanked for this. Seems like going out of your way to piss people off is the going business model these days.
  • Make more tests, take some pretty screenshots, put up a nice article on a site than can handle the slashdotting and you got yourself a great Slashdot article. This needs a lot more exposure than it gets right now.

    I know I'd read and comment to this if it was main page, I bet a lot of other Slashdotters think the same.

  • I've found Exchange Server does this, too.
  • I work for a company that provides enterprise level email filtering, and they are VERY serious about following up on mails sent to You should email hotmail support and let them know...
  • I don't know if it still does it, but does a seriously wrong thing with its HELO: it uses the right-hand-side of the email address for its HELO instead of an actual hostname. So if you send as, it sends a HELO of "" instead of your hostname. This trips an unbelievable number of spam filters. I personally special-cased this in Brightmail (what Hotmail uses) to exclude, but Hotmail also does its own thing, and might also have their spam threshold dialed way down -- st

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