If you're using a web-based email service (rather than a dedicated email client, such as Outlook Express, Thunderbird or Windows Live Mail) use an adblocker to prevent the ads showing in the first place. This is the most popular one:
https://adblockplus.org/
(However you won't have it running when using AB, will you? - 'Cos it will really annoy the Ed if you do!)
Many advertising-funded email services don't append advertising material to mail sent to dedicated email clients but, if yours does, you'll probably have to copy the text and then paste it into new word-processing document.