How to avoid spam filters

You have an engaging subject line, a beautifully designed email, and a great offer to send your customers. But will it reach their inbox? Before hitting send, you need to understand how to avoid the increasingly sophisticated spam filters and ensure your email will reach the recipients.

Every email server has filtering software to decide whether your email is junk. Here's a few things you need to be aware of.



Email service provider (ESP)

The most important factor in determining whether your message is marked as spam or not is your sender reputation score. This is associated with the IP address of the mail server you are using to send messages from. A brand new IP address with no history of email activity is regarded as suspicious because they don't know anything about the IP address that is being used to send the email.

It is therefore advisable to use an email service provider that has an excellent sender reputation to send your emails (e.g. MailChimp, dotMailer, Campaign Monitor) and one which protects its sender reputation by ensuring its clients don't send spam emails.

Email content

The content of your email is a significant factor in making it through spam filters. Subject header, image use and text content can all cause your email to be seen as spam.

Avoid these common mistakes:

  • Using words or phrases related to money, discounts or free offers.
  • Colouring fonts in bright colours.
  • Using all capital letters (especially in the subject line).
  • Excessive use of punctuation.
  • Check your image to text ratio. Too many images (or large images) compared to text can be considered as spam.

Unfortunately, there are too many to mention and the list continues to grow. But if you can avoid the above, you will increase the chances of your email being delivered.

Check before sending

Most email service providers have a spam checker tool which will scan your email for all the things spam filters look for. Running a spam test before you send your email is good practice.


It's as much about deliverability as it is about email performance. For help with your email marketing, call Karen on 07908 610 190 or email karen@sixothree.co.uk.