As a responsible B2B permission based email marketer, it is frustrating to find out that your custom crafted messages has been trapped by an overenthusiastic spam filter. While most server based spam filters are based on rules, pattern matching and bayesian filter engines, Microsoft Outlook has its own set of unpublished quirks which have been only partially understood.
There was a study conducted by MAPILab that looked at the inner workings of Outlook ‘03 and identified the type of checks being conducted including day of week the message was sent, time of day, delay between send and receipt, capital letters, repeat characters, select words etc. However, with Outlook ‘07, this has been further “improved” and there are instances where many previously compliant emails fail the new filter.
The only way to really be sure is to run tests by manually sending emails or to use services such as our Email Client Rendering and Spam Filter Tests. However adopting learnings from experience such as the one below can help reduce the number of iterations to get it right.
Our first test on this specific email passed on most email filters except Outlook ‘07. A review of the body revealed 6 instances of the word ‘Marketing’. Reducing this to 2 had no effect with the test again failing Outlook ‘07. A third test was done after changing the subject to a statement rather than a question ending in question mark.
1st and 2nd Spam filter test
3rd Test
This seemed to have that miraculous impact. It passed!
Outlook ‘07 places a lot of emphasis on the “?” and by extension other symbols (!,£,$,*) on the subject line. The best is to use a testing service or test directly on the client, but avoiding the above symbols on the subject line will save a few steps in getting it right.
The result - a 14% uptick on open rates and equivalent click through rates!
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