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by sethammons 2361 days ago
http://www.faqs.org/rfcs/rfc2821.html

SMTP RFC 2821 says that the local part of the email address is case sensitive. Some ignore this and consider upper and lower case the same.

Section 2.4:

> 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.
1 comments
toolslive 2361 days ago
same section, same RFC:

    > However, exploiting the case sensitivity of mailbox local-parts impedes interoperability and is discouraged.
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samatman 2361 days ago
These are of course not in conflict.

What it means is, a mailserver should resolve local part case-insensitively, so that Bob@example.com and bob@example.com end up in the same mailbox.

But, to be spec-compliant, a mailserver MUST send on an email addressed to AlIcE@example.net to AlIcE@example.net, exactly, without downcasing it to alice@example.net.

I'd imagine this is often honored in the breach, but there you have it.

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gowld 2361 days ago
"mail server" is ambiguous. SMTP Simple Mail Transfer Protocol is about transferring mail between domains, which must preserve the local part.

An MDA Mail Delivery Agent or LDA Local Delivery Agent inside a domain can choose whether to be case sensitive, but is discouraged from doing so.

The same issue exists for dots '.' in local part.

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