Does the content of my email matter for deliverability?

Absolutely. Ideally, you send email that people want. That’s over half the battle. In addition, you should make your content interesting and relevant to the recipient.

There are a few things to keep in mind about your email content. First, we suggest that you set up a test mailbox at Mailgun and enable our spam filters to receive a “spamicity” score to test how your content is being judged by spam filters. Here are some other things to consider:

  • Personalize your emails. Make sure to include the recipient’s address in the “To:” field and include his/her name in the greeting.
  • It is best to send multi-part emails using both text and HTML or text only. Sending HTML only email is not well received by ESPs. Also, remember that ESPs generally block images by default so HTML only will not look very good unless users are proactive about enabling images.
  • Test how your html email looks across all email clients and browsers.
  • Make your content relevant and targeted to the recipient.
  • The higher the text to link and text to image ratios, the better. Too many links and images trigger spam flags at ESPs.
  • Misspellings, spammy words (buy now!, Free!) are big spam flags, as are ALL CAPS AND EXCLAMATION MARKS!!!!!!!!!!!!!
  • The from field in your emails should match the domain you are sending from. Hotmail is particularly focused on this.
  • Make sure you are using unsubscribe links and headers in your emails. Many ESPs (particularly Hotmail) pay attention to this and if they are not there, you are likely to get filtered. You can always use Mailgun’s auto unsubscribe handling if you don’t want to deal with this on your end.
  • Include your physical mailing address. CAN-SPAM requires an unsubscribe link and a physical mailing list. It is also a good idea to provide a link to your privacy policy.
  • Gmail pays particularly close attention to Message ID and Received headers. Message IDs that are formed incorrectly (without brackets <> and with wrong domain after @) can make Gmail think you are a spammer. The simplest way to create the right Message ID is to not set Message ID at all. Then Mailgun will create a perfect Message ID for you. Also, if you use the HTTP API, Mailgun will deal with all of this for you.
  • Links should include the domain that is sending the email. Also, popular url shorteners can be a bad idea because they are frequently used by spammers.
  • Long links may cause bounces. Some ESPs will block emails with links (or any consecutive text) longer than 99 characters.