> Attempt to verify an email with a regular expression.

  .+@.+

That one always seemed sufficient for me, every issue after that is the users problem

Obviously there is a bit of nuance here, but the best rule of thumb is use a regex and then warn the user that it doesn't look valid but still accept it if it doesn't pass, and then send an email to verify it.

Except email addresses don't need to have an "@".

Is parsing HTML with regexes Ok?

No. See https://stackoverflow.com/questions/1732348/regex-match-open...

Roll your own encryption

Accept people's names

Anything