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Just adding my 2 cents as this is a configurable feature at least on 1.X.X branches of EE. In the admin, weblog management, weblog posting preferences section, you need to modify the “Automatically turn URLs and email addresses into links?” setting. If you want to be able to use HTML to link email addresses, then switch it to No. If you want EE to automatically attempt to encode any email address it detects then leave on the default value of Yes. I hope this helps someone out there.