Technically, there is no scientific nor explanation, nor solution for this, but there are ways to avoid it at least by a minimum. Rule number one is to put yourself in the recipients shoes and wonder – would I mark this as spam?
- Let your customers know that you will be sending them e-mails and when to expect those.
- Make it easy and visible for them to unsubscribe. You would rather want them to just leave the delivery list than let them mark your mails as spam.
- Make it recognizable from whom the mail is from. Use your brand and design techniques.
- The subject line and the content should go hand in hand – match. Otherwise, it would make the customer feel like a fool and definitely mark it as spam.