Are single quotes legal in the name part of an email address?

Question

For example:

jon.o\'conner@example.com ?

Answer 1

Yes, jon.o'conner@example.com is a valid email address according to RFC 5322.

From the Email address article at wikipedia (Syntax section):

The local-part of the email address may use any of these ASCII characters:

• Uppercase and lowercase English letters (a–z, A–Z)
• Digits 0 to 9
• Characters ! # $ % & ' * + - / = ? ^ _ ` { | } ~
• Character . (dot, period, full stop) provided that it is not the first or last character, and provided also that it does not appear two or more times consecutively (e.g. John..Doe@example.com).

(The syntax is formally defined in RFC 5322 section 3.4.1 and RFC 5321.)