What are valid and invalid email address characters

Question

What are valid and invalid email address characters in Exchange 2010, for example can you have Conan.O'[email protected] is there a document that shows the valid and invalid sysmbols?

Answer 1

Hi
    The format of email addresses is
local-part@domain where the local-part may be up to 64 characters long and the
domain name may have a
maximum of 253 characters - but the maximum 256 characters length of a forward or reverse path restricts the entire email address to be no more than 254 characters.<sup id="cite_ref-0">[1]</sup>
The formal definitions are in RFC 5322 (sections 3.2.3
and 3.4.1) and RFC 5321 - with a more readable form given in
the informational RFC 3696<sup id="cite_ref-1">[2]</sup>
and the associated errata.
Local part
The local-part of the email address may use any of these
ASCII characters
RFC 5322 Section
3.2.3:
Uppercase and lowercase English letters (a–z, A–Z) (ASCII: 65-90, 97-122)
Digits
0 to
9 (ASCII: 48-57)
Characters
!#$%&'*+-/=?^_`{|}~ (ASCII: 33, 35-39, 42, 43, 45, 47, 61, 63, 94-96, 123-126)
Character
. (dot, period, full stop) (ASCII: 46) 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. [email protected] is not allowed.).
Special characters are allowed with restrictions. They are:
o   
Space and
"(),:;<>@[\] (ASCII: 32, 34, 40, 41, 44, 58, 59, 60, 62, 64, 91-93)
The restrictions for special characters are that they must only be used when contained between quotation marks, and that 3 of them (The
space, backslash \ and
quotation mark " (ASCII: 32, 92, 34)) must also be preceded by a backslash
\ (e.g.
A quoted string may exist as a dot separated entity within the local-part, or it may exist when the outermost quotes are the outermost characters of the local-part
(e.g. abc."defghi"[email protected] or
"abcdefghixyz"@example.com are allowed. Conversely,
abc"defghi"[email protected] is not; neither is
abc\"def\"[email protected]). Quoted strings and characters however, are not commonly used.
RFC 5321 also
warns that "a host that expects to receive mail SHOULD avoid defining mailboxes where the Local-part requires (or uses) the Quoted-string form".
The local-part "postmaster" is treated specially - it is case-insensitive, and should be forwarded to the server's administrator. Technically all other local-parts
are case sensitive, therefore [email protected] and [email protected] specify different mailboxes. However most organizations treat uppercase and lowercase letters as equivalent, and also do not allow use of the technically valid characters
(space, ? and ^). Organizations are free to restrict the forms of their own email addresses as desired, e.g.,
Windows Live Hotmail,
for example, only allows creation of email addresses using alphanumerics, dot (.), underscore (_)
and hyphen (-).<sup id="cite_ref-2">[3]</sup>
Systems that send mail must be capable of handling outgoing mail for all valid addresses. Contrary to the relevant standards, some defective systems treat certain
legitimate addresses as invalid and fail to handle mail to these addresses. Hotmail, for example, refuses to send mail to any address containing any of the following standards-permissible characters:
!#$%*/?^`{|}~
Domain part
The domain name part of an email address has to conform to strict guidelines: it must match the requirements for a
hostname,
consisting of letters, digits, hyphens and dots. In addition, the domain part may be an
IP address
literal, surrounded by square braces, such as jsmith@[192.168.2.1], although this is rarely seen except
in email spam.
Examples
Valid email addresses
<tt>[email protected]</tt>
<tt>[email protected]</tt>
<tt>[email protected]</tt>
<tt>much."more\ unusual"@example.com</tt>
<tt>very.unusual."@"[email protected]</tt>
<tt>very."(),:;<>[]".VERY."very@\\\ \"very"[email protected]</tt>
Invalid email addresses
<tt>Abc.example.com</tt> (an @ character must separate the local and domain parts)
<tt>[email protected]</tt> (character dot(.) is last in local part)
<tt>[email protected]</tt> (character dot(.) is double)
<tt>A@b@[email protected]</tt> (only one @ is allowed outside quotation marks)
<tt>a"b(c)d,e:f;g<h>i[j\k][email protected]</tt> (none of the special characters in this local part
is allowed outside quotation marks)
<tt>just"not"[email protected]</tt> (quoted strings must be dot separated, or the only element making
up the local-part)
<tt>this is"not\[email protected]</tt> (spaces, quotes, and backslashes may only exist when within
quoted strings and preceded by a slash)
<tt>this\ still\"not\\[email protected]</tt> (even if escaped (preceded by a backslash), spaces, quotes,
and backslashes must still be contained by quotes)
Terence Yu
TechNet Community Support