Don't use all caps anywhere in your email or its subject line.
Don't embed forms in your emails; send recipients to a landing page on your site instead.
Don't use spam trigger words like "free," "guarantee," and "no obligation" in your subject line or email body. These are spam trigger words, and will see you junked.
List of Spam Trigger Words
Don't use a red font when drafting your email. Also do not use white font on top of a white background.
Don't use exclamation points!!!!!
Don't forget to use spell check; misspellings and bad grammar are yet another spam indicator in your email copy.
Don't jam pack your email copy with search / marketing keywords.
Don't use tons of images, or very large images.
And remember, all images should have associated alt text!
Don't include attachments to your emails. Just as with landing pages, send recipients to a page on your site to download whatever it is you want to send.
Or use a file sharing tool such as Dropbox or Google Drive
Do ask your contacts to whitelist you and add you to their address book.
Spam filters are more aggressive than ever, and sometimes email people value still end up in spam boxes.
By asking your subscribers to add you to their address book, it tells spam filters to back off.
Do include a clear unsubscribe link and a physical mailing address in your signature block.
If you are sending bulk-marketing email, a functional unsubscribe link is the law.
Do include your recipient's name in the 'To:' field so spam filters know that you do, indeed, know your recipient.
Use the address book in outlook properly, and this will be automatic.
Do keep emails short; too much text is another red flag for spam filters.
Do include the date somewhere in the body of your email to show your message is current.