Login to your account via webmail and delete the offending message on the server.

When you say log into my webmail account, which account are you referring to? My inbox in this mozilla support forum shows no emails in my inbox.

This forum has nothing to do with your email. Log into your providers webmail page and delete the problem mail.

I logged into my email account at my provider. The email doesn't show up in any of my folders there once I have deleted it from my Thunderbird inbox. I have Thunderbird set to delete it from my providers server when I delete it on my computer which it appears it is doing. So where on the webmail server do you suggest I look?

That is where you were to look then you said you had nothing in your Inbox on this forum.

My provider is Xfinity. I have an email account there. I can go to that account and see if there are emails still there. I also have an email account on this forum. And finally I have an inbox, email using Thunderbird. I am receiving the unwanted email on my Thunderbird email account. I erase in each time and also erase it in the deleted folder. Because of an earlier suggestion I went to Xfinity to see if there was anthing there.

So to further clarify, there is no copy of the offending email at the Xfinity server, in the forum emal account and no email in my Thunderbird program. So where are you suggesting that I go to delete the email?

The notifications@suppport.mozilla.org emails is being sent to your @comcast email you used to register your Mikeellenstein account here.

Look at top where it should say "Ask a question Contributor Mikeellenstein Inbox"

Click on Mikeellenstein > EDIT SETTINGS > uncheck anything you do not want emails sent for and then click on Update button.

Of the three that you listed only Xfinity is an email provider with real email accounts. The is no email account on this forum and there sure is no Thunderbird email account. So Xfinity would be your email provider with a webmail page.