Candy wrote:

1. The situation I first described was only one email, one time.
2. I said, “Outlook would not let me send”, because that is just what
happened. I did not know how else to describe it. I am not an expert. That
is why I come to this group – looking for answers.
3. I believe the email address came either from an esnips page or from
another web site on which I was searching for some help.
4. I did not save the email after I discovered it was no longer a valid
email address.
5. When I first hit the send button – NOTHING happened. It just hung there
– wouldn’t send, wouldn’t go, wouldn’t do anything. It was frozen. I had
never had that happen before this time.
6. I do not recall if it moved to the outbox or not. I know it is not there
now, because I deleted it.
7. It never went to the sent folder because it never sent. It just hung
there – wouldn’t send, wouldn’t go, wouldn’t do anything. It was frozen.
8. This was my first occasion after the computer crash and recovery that I
had had an email problem.
9. The email address I entered in the to field appeared to be valid (it
appeared to have all the proper parts that an email address should).
10. I do not recall any error message. This is why I was puzzled. I could
not figure it out.
11. Then I used the link I described in my previous message to check and see
if the email address was still active. It was not. I assumed that that was
why it did not send.
12. If you do not have enough information, then ask questions, like you did
just now. I did not know how else to describe the situation. I am not an
expert. That is why I come to this group – looking for answers.

It appears you have an add-on that hung (which took Outlook with it).
Many anti-virus programs install their add-on to provide for their
superfluous e-mail scanning feature. You can see what add-ons are
installed in Outlook. To test if an add-on is causing problems with
Outlook, you can load Outlook in its safe mode ("outlook.exe /safe")
which does not load any enabled add-ons.

I'm basing my guess on your mention that Outlook hung. That it was
working before and "suddenly failed" (even with a claim that you did not
change anything yourself) doesn't mean that Outlook or its add-ons did
not change. AV (anti-virus) programs get updates. Sometimes those are
*program* updates and not just signature updates. When the AV program
changes, its behavior can also change. So what was working before that
suddenly stopped working without you changing anything could be due to
an auto-update that changed Outlook (via Windows Updates) or changed an
add-on (like an AV add-on).