Email List Hygiene — Part 2: Best Practices to Avoid Spam Filters

Part one of this series on email list hygiene dealt with the difference between spam traps and spam filters. Where spam traps are email addresses used as bait for spammers, spam filters are applications and algorithms which can identify and stop spam from ever reaching an inbox. Now we can move on to some strategies.

Avoiding spam traps is easy: just don’t buy email lists. Spam filters are trickier since it is all about the content in your email message. What you write and how it is written have a huge impact on whether your emails are marked as spam or not.

Proofread Your Messages

Faulty grammar and spelling will always look unprofessional so even disregarding spam, it just makes sense to proofread. Having said that, spelling errors and grammatical mistakes are also big spam triggers. In the early days, spammers would use misspelled words as a way to get past filters so they now look for these mistakes.

Don’t Use Capital Letters

A simple thing to avoid is the use of all caps, especially in subject the subject field since it is the online equivalent of yelling at the receiver. No one likes being screamed at. Users are more likely to mark all-caps messages as spam and spam filters also use words written in all capital letters as a trigger.

Avoid Symbols and Excessive Punctuation

Another trigger for spam filters is using multiple exclamation points or excessive use of any other punctuation mark— especially the dollar sign ($) which should be avoided. While an exclamation mark is a good way to attract attention to your email’s title in an inbox, studies have shown question marks actually do better. So if you want to put in a punctuation mark it’s better to make a subject that asks a question.

Watch for Spam-like Phrases

There are words that trigger spam filters which should be avoided. The most obvious ones are Viagara and Cialis as well as common misspellings (v1agara c1al1s) but there are quite a few more that might surprise you. Phrases like “click here” or “lower monthly payment” can trigger the spam filter and even words like “cash” or “free” should be avoided. has put together an extensive list of 455 words and phrases to avoid.

Clean Text and Colour

Spammers try to get attention or hide text through various means. Using colour on text, overusing underlined and bolded text, or even large font sizes to draw the eye will be flagged by the filters. Similarly, some spammers try to hide text by making it small or colouring it white on a white background so text that is too small will also be flagged. Try to use standard font sizes in your emails.

There is a lot more you can do to avoid the spam filter and we’ll continue on with part three of this series.

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