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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'Brian@email.com is there a document that shows the valid and invalid sysmbols?
    • Moved by Sean Jenkin Friday, January 06, 2012 6:20 PM (From:MSDN, TechNet, and Expression Profile and Recognition System Discussions)
    Friday, January 06, 2012 2:37 AM

Answers

  • 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. John..Doe@example.com 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".xyz@example.com or "abcdefghixyz"@example.com are allowed. Conversely, abc"defghi"xyz@example.com is not; neither is abc\"def\"ghi@example.com). 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 jsmith@example.com and JSmith@example.com 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>niceandsimple@example.com</tt>

    ·        <tt>a.little.unusual@example.com</tt>

    ·        <tt>a.little.more.unusual@dept.example.com</tt>

    ·        <tt>much."more\ unusual"@example.com</tt>

    ·        <tt>very.unusual."@".unusual.com@example.com</tt>

    ·        <tt>very."(),:;<>[]".VERY."very@\\\ \"very".unusual@strange.example.com</tt>

    Invalid email addresses

    ·        <tt>Abc.example.com</tt> (an @ character must separate the local and domain parts)

    ·        <tt>Abc.@example.com</tt> (character dot(.) is last in local part)

    ·        <tt>Abc..123@example.com</tt> (character dot(.) is double)

    ·        <tt>A@b@c@example.com</tt> (only one @ is allowed outside quotation marks)

    ·        <tt>a"b(c)d,e:f;g<h>i[j\k]l@example.com</tt> (none of the special characters in this local part is allowed outside quotation marks)

    ·        <tt>just"not"right@example.com</tt> (quoted strings must be dot separated, or the only element making up the local-part)

    ·        <tt>this is"not\allowed@example.com</tt> (spaces, quotes, and backslashes may only exist when within quoted strings and preceded by a slash)

    ·        <tt>this\ still\"not\\allowed@example.com</tt> (even if escaped (preceded by a backslash), spaces, quotes, and backslashes must still be contained by quotes)


    Terence Yu

    TechNet Community Support

    • Proposed as answer by Richard MuellerMVP Wednesday, January 11, 2012 1:10 AM
    • Marked as answer by Terence Yu Friday, January 13, 2012 3:04 AM
    Monday, January 09, 2012 2:34 AM

All replies

  • Ask in an Exchange forum, for example similar questions have been asked here:

    http://social.technet.microsoft.com/Forums/en/exchangesvradmin/threads

     


    Richard Mueller - MVP Directory Services
    Friday, January 06, 2012 3:03 AM
  • On Fri, 6 Jan 2012 02:37:55 +0000, amperch wrote:
     
    >What are valid and invalid email address characters in Exchange 2010, for example can you have Conan.O'Brian@email.com
     
    Yes, you can. An apostrophe in the <local-part> of the e-mail address
    is acceptable.
     
    >is there a document that shows the valid and invalid sysmbols?
     
    RCF821, RFC2821, etc. define the character set used to construct valid
    SMTP addresses.
     
    ---
    Rich Matheisen
    MCSE+I, Exchange MVP
     

    --- Rich Matheisen MCSE+I, Exchange MVP
    Saturday, January 07, 2012 2:53 AM
  • This pretty much still applies. - http://support.microsoft.com/kb/841091


    Sukh
    Sunday, January 08, 2012 10:58 PM
  • 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. John..Doe@example.com 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".xyz@example.com or "abcdefghixyz"@example.com are allowed. Conversely, abc"defghi"xyz@example.com is not; neither is abc\"def\"ghi@example.com). 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 jsmith@example.com and JSmith@example.com 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>niceandsimple@example.com</tt>

    ·        <tt>a.little.unusual@example.com</tt>

    ·        <tt>a.little.more.unusual@dept.example.com</tt>

    ·        <tt>much."more\ unusual"@example.com</tt>

    ·        <tt>very.unusual."@".unusual.com@example.com</tt>

    ·        <tt>very."(),:;<>[]".VERY."very@\\\ \"very".unusual@strange.example.com</tt>

    Invalid email addresses

    ·        <tt>Abc.example.com</tt> (an @ character must separate the local and domain parts)

    ·        <tt>Abc.@example.com</tt> (character dot(.) is last in local part)

    ·        <tt>Abc..123@example.com</tt> (character dot(.) is double)

    ·        <tt>A@b@c@example.com</tt> (only one @ is allowed outside quotation marks)

    ·        <tt>a"b(c)d,e:f;g<h>i[j\k]l@example.com</tt> (none of the special characters in this local part is allowed outside quotation marks)

    ·        <tt>just"not"right@example.com</tt> (quoted strings must be dot separated, or the only element making up the local-part)

    ·        <tt>this is"not\allowed@example.com</tt> (spaces, quotes, and backslashes may only exist when within quoted strings and preceded by a slash)

    ·        <tt>this\ still\"not\\allowed@example.com</tt> (even if escaped (preceded by a backslash), spaces, quotes, and backslashes must still be contained by quotes)


    Terence Yu

    TechNet Community Support

    • Proposed as answer by Richard MuellerMVP Wednesday, January 11, 2012 1:10 AM
    • Marked as answer by Terence Yu Friday, January 13, 2012 3:04 AM
    Monday, January 09, 2012 2:34 AM
  • Hi
       Do you have any update on your thread ?

    Terence Yu

    TechNet Community Support

    Wednesday, January 11, 2012 12:57 AM