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  1. #1
    Super Moderator BATcher's Avatar
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    Feb 2008
    A cultural area in SW England
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    Capital letters in local part of email addresses

    (I'm afraid this question is about email, not Outlook, but is seems to be the closest forum...)

    Has anyone experienced a problem where emails sent to
    are rejected 'somewhere', whereas emails sent to
    are accepted?

    The only problem I've ever had with mixed-case email addresses is with sending to, about 18 months ago, and I haven't had occasion to try since.

    I am aware that the RFC 2821, the standard that defines how email transport works, says: The local-part of a mailbox MUST BE treated as case sensitive. Therefore, SMTP implementations MUST take care to preserve the case of mailbox local-parts. Mailbox domains are not case sensitive. In particular, for some hosts the user "smith" is different from the user "Smith". However, exploiting the case sensitivity of mailbox local-parts impedes interoperability and is discouraged.

    However, in the very many years since the standard was written, the convention seems to have become that UpperCase characters are acceptable in the 'local part' of the email address.

    Can anyone give recent real examples where this does not apply?

    milliHelen (sub-unit): that quantity of female facial beauty sufficient to launch a single ship

  2. #2
    Gold Lounger Roderunner's Avatar
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    Dec 2009
    Thanked 218 Times in 185 Posts
    Hi BATcher, any time I was creating an email address, regardlessly of which one I was starting i.e. gmail or hotmail, I always used lower case and when adding one to my contacts list. I have never had any trouble sending mail. I started originally with AOL Mail till I found W L Mail.
    O wad some Power the giftie gie us, to see oursels as ithers see us!

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