How to prevent your message from being marked as spam or junk mail

To check your message's junk mail score:

Choose Message > Check Junk Mail Score...

Images

Messages that consist primarily of one large image (or many images) and very little text are usually considered to be spam. Resist the urge to package your email up into one large image, and instead create a proper HTML message with text and images.

Subject

Make sure your message includes a subject line. Emails without subject lines are frequently marked as spam.

Plain Text Alternative

By default, Direct Mail will automatically include a plain-text version of your email for those recipients that can't receive HTML email. If you override this and create your own plain-text alternative, make sure that the content does not differ too wildly from the HTML version. If the HTML and plain-text versions differ greatly, your message could be marked as spam.