I got an error message while attempting to send a private message (in fact, I got the same error message three times because I retried the "send"):
Error sending. Error sending copy to sender.
I can confirm that I (as sender) didn't receive a copy of the message, but I don't know if this error message means that the intended recipient also didn't get the message. And I don't know if this is just a problem for me or if it's happening WikiTree-wide.
Emails should be back to normal now.