When logging in to usermin (haven’t checked with Webmin or VIrtualmin), someusername@example.com would work but SomeUsername@example.com won’t. Shouldn’t the username field be case insensitive?
Users on Linux are always case sensitive.
I think that’s correct behavior, but I guess I can see how one might want it to behave otherwise…but, technically, I don’t know how we’d accomplish that without forcing normalization on the names (i.e. lowercase them before saving and lowercase when comparing). That seems more surprising than case sensitivity.
The tricky bit: email addresses are always case insensitive. 
That login sure looks like an email address…
To go further:
However, due to the email issue, best practice is always treat as lower case.
Imagine email to MrPete@… How could the system choose the mailbx
The comment on that help text doesn’t go far enough.
RFC’s require email mailbox name handling to be case-insensitive, period.
Can you send the source url for this RFC because I google it and cannot find it.
I did a quick search, and this is as close to a well-documented set of answers I could find. smtp - Are email addresses case sensitive? - Stack Overflow
To summarize: Domain names must be case insensitive, which in practice means they should always be lowercase. Usernames may or may not be case sensitive, but you have no guarantee that all mail systems will respect that case sensitivity and you almost certainly should not do it, even if your local system supports it. Odds are good you would reduce deliverability with case sensitive usernames.
My advice is just use lowercase for everything. Going back to the actual subject of this topic, Usermin could, I guess, be modified to allow case insensitivity, but my gut tell me that’ll just make people more likely to make messes for themselves.
So all good 
TYPO alert: 4343 not 2343. (I googled: rfc case insensitive hosts 
)
For any RFC (IETF standards docs) just google: RFC and the number. so, rfc 4343…
That gives a link to RFC 4343 - Domain Name System (DNS) Case Insensitivity Clarification
Just want to point out that RFC applies to domain/host names, not email usernames.
But, still, my gut tells me you’re better off sticking to lowercase for usernames, too.
(sorry for the RL delay )
Since an email address includes both (username and domain/host name), that’s why it’s best, and yes @Joe, your gut is informing you well.
Over time, I’ve seen all kinds of painful email network/relay rewrites out there, including conversion to all uppercase. Bleah.
Just not worth the hassle to try to support mixed case in this context.
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