[toolslive]

BUT, I've seen case sensitive interpretation of email addresses on a microsoft mail server. (no kidding)

[sethammons]

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.

[toolslive]

same section, same RFC:

    > However, exploiting the case sensitivity of mailbox local-parts impedes interoperability and is discouraged.

[samatman]

These are of course not in conflict.

What it means is, a mailserver should resolve local part case-insensitively, so that [e-mail] and [e-mail] end up in the same mailbox.

But, to be spec-compliant, a mailserver MUST send on an email addressed to [e-mail] to [e-mail], exactly, without downcasing it to [e-mail].

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

[gowld]

"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.

[StuffedParrot]

Email addresses are case sensitive, at least you’re supposed to assume they are.

[lgats]

Are there any widely-used, case-sensitive, public or corporate email servers?

I've certainly strtolower'ed some email inputs...

[sethammons]

See my link to the RFC in a sibling comment. You should not strtolower an email address unless you are the one running the mailbox itself.