Yesterday was a total waste.
When I turned on the computer, the screen told me that Microsoft was desperate to do an update. So I clicked the okay button and went off to do chores. When I came back an hour later; I discovered that MS was knee deep into upgrading me to Windows10. I decided not to abort the operation.
The computer took until 4:30PM to complete the upgrade. A whole day wasted on an upgrade.
To make matters worse. While the upgrade was running, I discovered that something was horribly wrong with my email set up and I couldn't fix the problem because my computer was knee deep in an upgrade.
(Mental note: One of these days I should get a second computer.)
I wasn't able to debug the email problem until 9PM. At 11:00PM I finally figured out the problem. In the MX record on plusroot.com, I had used the default value for priority which was 0. Apparently this is invalid. The mail worked for the first few days, but the invalid entry propagated and blocked incoming email.
I've concluded that the two most important steps in diagnosing email are (from a Unix terminal):
First use the telnet command to log into the computer to see if you can send an email manually.
telnet example.com 25
If you can send the email, then use the dig command to check the MX record:
dig example.com MX
I am now waiting to see if the changes I made to the MX record propagate through the system correctly.