Leading underscores in an email address?
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18-05-2021 - |
Question
What RFC would I refer to in order to find out if a leading underscore in the local part of an email address is acceptable?
Example: _johndoe@hotmail.com
Of course, this question can also apply to any leading special character.
I found this line in Wikipedia, but couldn't find any reference within the RFC itself. Did I miss something here?
Local part The local-part of the email address may use any of these ASCII characters RFC 5322 Section 3.2.3:
Solution
Quoting RFC5322.
Section 3.4.1 says:
An addr-spec is a specific Internet identifier that contains a
locally interpreted string followed by the at-sign character ("@",
ASCII value 64) followed by an Internet domain. The locally
interpreted string is either a quoted-string or a dot-atom.
Going back to 3.2.3 you get:
atext = ALPHA / DIGIT / ; Printable US-ASCII
"!" / "#" / ; characters not including
"$" / "%" / ; specials. Used for atoms.
"&" / "'" /
"*" / "+" /
"-" / "/" /
"=" / "?" /
"^" / "_" /
"`" / "{" /
"|" / "}" /
"~"
atom = [CFWS] 1*atext [CFWS]
dot-atom-text = 1*atext *("." 1*atext)
dot-atom = [CFWS] dot-atom-text [CFWS]
[CFWS] means comment or whitespace.
So the first part of an email address can be a dot-atom, which in turn begins with an atext, which can be an underscore.
Yes, an email address can begin with an underscore.
OTHER TIPS
Section 3.4.1 of that RFC defines how addresses are specified and references things defined in section 3.2.3. There's nothing that prohibits a leading "_".