Emails sent via Special:EmailUser will now show up with a From address
of <wiki(a)wikimedia.org>rg>, instead of the user who sent the email. This is
to work around DMARC restrictions that affected some users depending
on their email provider (I think Yahoo was most affected).
The Reply-to address will still be set to the email address of the
sender, so pressing "reply" in your email client will continue to work
as expected. In addition, the footer message is a little more explicit
that by replying, you are revealing your email address.
This should make the Special:EmailUser service more reliable, I hope.