foo must be an email address

MUST conform to the "addr-spec" production in RFC 2822

Convert the email address to a valid form. Examples of valid email addresses:

• joesmith@example.com
• joesmith+nospamplease@nospam.example.com

Note: addr-spec does not include a provision for a display-name. Use atom:name instead. Examples of invalid email addresses:

• joesmith@example.com (Joe Smith)
• Joe Smith <joesmith@example.com>