Your pet peeve, technical or otherwise.

[kjpye]

No, the DNS is case-insensitive. Therefore anything after the '@' can be any case you like, and you can change it in each message if you wish. The part before the '@' may or may not be case sensitive at the behest of the mail user agent on the mail receiving server. Thus sites which convert everything to upper- or lower-case are wrong, but very common. (Gmail for example is case-insensitive in that part as well, but you shouldn't extrapolate from that.)

[PlainName]

Email is not case sensitive after the @, so could be upper or lower or mixed case. Generally, the stuff before the @ isn't case sensitive but could be.

See https://datatracker.ietf.org/doc/html/rfc5321

Rationale: the stuff after the @ is a DNS name so cannot be case sensitive. The stuff before the @ depends entirely on the local mail server and client, so who knows what goes on there.

[RJSV]

Ah!  Thank you.  I'm surprised that I didn't even know this, before.
   Usually, I just try sending, but it can get to be a waste of time, (when the daemon replies with 'no such address, could not be delivered, but maybe that was because there were other basic errors in my spelling.

[MathWizard]

Wow, actually Microsoft did the right thing, and updated my win10, so that now I can finally disable the news feed on the look screen.

The option to disable it was missing from my version, even tho it updates all the time. And I tried some powershell method, and that didn't work either.

But MS freed me, and now my very powerful PC, boots up fast again.