Ensure HTML and Plain Text Parts Have Corresponding Content

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Sending your email newsletters and marketing campaigns multipart/alternative gives you the best of both worlds: you can send richly formatted messages, but your recipients can opt for the plain text if they prefer.

Make Sure HTML and Plain Text Have Corresponding Content

Spammers like to fool junk mail filters by inserting random words, poems, and whatnot, possibly in the plain text part only so that the majority of recipients will never see them.

To counter this trick, some spam filters check whether the contents of the text/plain and the text/html parts do match. To make sure your message is not regarded as spam, make sure this is so. Of course, you can include a link to a full-graphic version on your website in the plain text part.