May 23, 2016
Posted by Robert Creech in: May Contain Nuts
As discussed in my previous article, there seems to be an increasing chance of genuine email getting quarantined by spam filtering tools as the battle to protect against unwanted or harmful content continues.
When investigating a ‘lost’ outbound email we often arrive at the point where we can prove an email arrived to the recipient’s system but, if managed by others, we can offer little more in terms of how that mail was then processed. There are some simple techniques which can help you limit the chances of your own mail becoming a ‘false positive’, quarantined in error.
– Consider the number of recipients – some filters will interpret a high number of recipients as an indication of spam
– Ratio of text to image – word filters can’t ‘read’ an image so spammers often send images containing a visible written message. Some filters may be set to score a mail as potential spam based upon the text to image ratio
– HTML code and links in emails – a link or two should not be enough to trigger most filters but may contribute to the overall score. A mail full of links may well fail with some filters
– Email subject length – an overly long subject will almost always contribute to a spam score so remain concise
– Reply and forward prefix – decent mail systems add a prefix of “Re” to replies and “Fwd” to forwarded mail just the once. If already present in a conversation they shouldn’t be added a second time. Unfortunately some mail systems seem to ignore this protocol so the subject length is artificially lengthened with multiple repetition of “Re” before getting to the original mail subject. Delete unnecessary content from the subject to remain concise
– Subject format – TYPING THE SUBJECT IN CAPITALS triggers many filters
– Mail content – think about what phrases may be used in spam mails. I apologise in advance for the example but my go-to demonstration for this is a gym which sent out a mail shot including the phrase, “if your new year’s resolution is to shed some extra inches off your waistline, come in and…”. The inclusion of the phrase “extra inches” was enough to trigger many spam filters based upon other, common junk mails
– Attachments – 10Mb still seems a pretty reasonable guide for maximum email size. Some systems allow more but many don’t. Filters are also getting more picky about attachments in general. It may prove better where possible to have the would-be attachment hosted securely on-line so the email need only contain a link from which the recipient can download
Keep in mind that one cannot control how the external recipient’s system will process a delivered email. One can, however, increase the chances of the sent email arriving into the destination mailbox.
If you would like any further help or advice with regard to email, filtering options or security please get in touch.