Answer by grosser for How can I validate an email address using a regular expression?

This rule matches what our postfix server could not send to.

allow letters, numbers, -, _, +, ., &, /, !

no -foo@bar.com

no asd@-bar.com

/^([a-z0-9\+\._\/&!][-a-z0-9\+\._\/&!]*)@(([a-z0-9][-a-z0-9]*\.)([-a-z0-9]+\.)*[a-z]{2,})$/i