Internet Service Providers and Email Service Providers will scan the content of emails to determine the likelihood of that email being spam. The most common flags are:
- Personalization: Personalize your email with merge fields. A recipient will be less likely to flag an email as spam that has been personalized to their name/role/etc.
- CTA: Emails that have a more successful impact clearly call out the action you want the recipient to make. Make sure you are also calling out the benefit they are getting from the action.
- Email has too many images and not enough text: Spam filters can’t read images and scammers know this, so they will often include a large image in their email. However, spam filters these days know this and will outright block an email if it includes lots of images and little text.
- Suspiciously formatted emails: If your email contains suspicious elements such as an overuse of unsupported HTML tags, mismatched links, or strange formatting it could be flagged as spam.
- If your email sending frequency is too high: Sending emails to a lot of recipients who you otherwise would receive no response back, or could be reported as spam, can result in future emails being flagged as spam to those senders or by that email server
- Microsoft Outlook has a filtering and reputation system of their own in addition to typical spam filters. If a specific email address sends a lot of emails but doesn't get any replies, its reputation score decreases and it is eventually tagged as a spam/junk sender.
Checking Email Content
There are many services that exist online that check the "Spammyness" of your email by comparing it against known triggers. One free alternative is mail-tester which checks against SpamAssassin, an open source and widely used spam filter. Paid services offer more universal checks and analytics features.