Spam Filters


Where do they come from
Every recipient of emails today has a spam filter on their account.
This is either supplied by the ISP or it is a third party plug-in to an email client ie Outloook or Outlook express.
These filters will check every detail of the email before it gets to the inbox and decide whether or not it is bulk, spam or a proper email.
Many corporate filters have different levels of filtering which can be decided by the network administrator and/or the direct user.
Many of the higher levels will directly target and block newsletters.

Safe List
The best way to get in the inbox is to have your sending email address in the recipients’ address book with the ISP and/or specified safe list, these are often the same thing. It is corporate filters which will have an additional safe list/
This means to the email handler that any email from this sender is expected as they are already a contact. So it essentially skips the deep filtering.

Pure Spam Tester
Our spam tester with Spam assassin picks up most of the issues and reports them but some of the explanations are not clear – I have yet to compile an explanation of these issues.
Normally it’s OK to send when there are one of two low warnings. It is best to resolve the medium warnings as they are usually easily fixed. Try to avoid sending any email with any high warnings as these will get a very poor delivery rate but will still spend credits.

Plain Text Comparison
One of the most important things to remember is to make sure there is a plain text version and that the amount of text content in the html version is reflected in the plain text version.
Many filters will take both versions, strip the html out of the html version and then count the amount of characters in each and if they do not relate fairly closely they will not get in the inbox.
A good example of this is reflected in our own esales setup. The plain text version of a lot of the esales templates can only have the hyperlink to the html version because the content can be changed in the VE and will there for not be the same in the plain text version if there was any predefined content. This is often why quotes do not get in the inbox. There is a solution to this but that is for another post!

Max Lines Error
“Message lines too long – MAX 1000”.
So either there can only be a maximum of 1000 characters before someone presses enter in an email. OR onlt 1000 lines of text? Can’t find it on Google though!
This was illustrated in the LetsRecycle report on 1st December 2006 16.30.
This was a perticularly long email too!

Low Errors
Some corporate filters are now stopping all errors, even the low ones:
Technical Bit
Unfortunately, if there are any tables in the html, our editor automatically adds <tbody> tags inside the <table> tags. This is unfortunate but will always give a warning and will not get in a very small percentage of inboxes.
It is unlikely that we will be changing the VE in the near future but as we have to parse the html in order to add our mailid and tracking details to the message it may be possible to delete the <tbody> tags on the way through

Image size
Another classic warning is the size of images.
We all know that people like to click images as links instead of hyperlinks but if there is a large picture it will get a warning. Large Images should be broken down into little images – like a jigsaw.
A good example of the wrong way to do it is Eurodivision’s ‘Offers final’. – a giant picture with all of the offers on it. They have been informed that on the rare occasion that they do get in the inbox no-one will click through and it looks like spam!