A couple of weeks ago I wrote about the top ten email campaign tips to get your message through to the user’s inbox. The last hurdle in this process is the spam filter, which warrants more explanation about how it works.
SpamAssassin is one of the leading open source spam filters that is widely used, and will serve as our example product about how it figures out if a message is spam or not. When a message comes in, it examines its content, structure, and format and applies a series of rules to evaluate it. Each rule has a number of points associated with it, which can be modified by each email administrator. The default setting is that if a message has more than five points, it is considered spam.
Here are some of the rules and their default point values:
|
Rule |
Points |
|
Structure |
|
|
Html and text content within the email differ |
0.739 |
|
Message only has html part |
1.457 |
|
Delivered by host with no reverse DNS entry |
0.1 |
|
From is blank |
0.760 |
|
From starts with numbers |
1.499 |
|
Header contains unclosed bracket |
2.206 |
|
Date header differs from received time |
0.44 to 3.199 depending on difference |
|
Very long headers |
2.5 |
|
Missing blank line between header and content |
2.5 |
|
|
|
|
Content |
|
|
80% or more blank lines |
1.0 |
|
Https link to ip address instead of domain name |
2.897 |
|
Talks about price per dose |
1.623 |
|
“no perscription needed” |
2.619 |
|
Subject has ! and ? |
1.390 |
|
Subject contains G.a.p.p.y-T.e.x.t |
1.020 |
|
Subject contains “as seen” |
1.000 |
|
Subject starts with dollar amount |
1.421 |
|
Subject contains “Your family” |
1.043 |
|
Subject contains “Your bills” |
2.622 |
|
Subject talks about losing pounds |
1.466 |
|
Subject is all caps |
2.077 |
|
Local part of the To: address appears in subject |
2.020 |
|
HTML content font color similar to background color |
0.124 |
|
HTML font face is not valid |
0.884 |
|
Includes html form to send email |
1.0 |
|
Has images with words in them |
1.526 – 2.460 depending on quantity |
|
Malformed HTML |
0.994 – 1.334 |
|
Contains “Dear “+ something (old letter greeting) |
1.605 |
|
Talks about lots of money |
0.63 – 1.875 |
|
“ACT NOW” |
.0792 |
|
“guaranteed!” |
0.939 |
And hundreds more! See a complete list at SpamAssassin
If your message looks like spam, it probably is. If you want to get your message through to the inbox, use a system that will take care of the structure components properly, like TrackVia’s Email Campaign feature. Then send content that isn’t spam and doesn’t look like spam according to these rules.
