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.
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This is one good reason why
- you should make sure the basic content of both parts is approximately the same.
But there's another, maybe just as convincing one: spam filters.
Spammers like to fool junk mail filters by inserting random words, poems and what not, 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 web site in the plain text part.
