Valid email addresses with + (plus symbol) are considered "invalid"

My new email address contains + (the plus symbol), but Wells Fargo's online banking website says this email address is invalid.

According to RFC 3696 §3 (and also RFC 2821 and RFC 2822):

Contemporary email addresses consist of a "local part" separated from a "domain part" (a fully-qualified domain name) by an at-sign ("@").

[...] Without quotes, local-parts may consist of any combination of alphabetic characters, digits, or any of the special characters

! # $ % & ' * + - / = ? ^ _ ` . { | } ~

[...] Stated differently, any ASCII graphic (printing) character other than the at-sign ("@"), backslash, double quote, comma, or square brackets may appear without quoting.

The website needs to be updated so that it allows email addresses containing + as well as the other special characters, as they indeed constitute valid email addresses. :-)