The more HTML content the email has, the more chances of the email going into the recipient's junk mail and until they put your email to their safe contact list it will stay there. Examples of HTML content: logos, tables, designed emails.

The simpler the email template, the better the chances of it not getting intercepted as junk.

There are some other factors to consider:

  1. Personalise your emails, do not say "Dear Customer", but use their name "Dear Mr James.

  1. Enter a sensible subject that sounds personal and natural, sometimes entering promotional language like "*** WIN, FREE, PROMOTION***" can cause your email to be immediately flagged as junk mail.