BK, I'm very happy your emails havbe turned up. My problem was the server. When my Mac man set up my first computer in 2001, he put my email server on Netscape. When Netscape went under, he told me how to move to SeaMonkey, which is now - according to Apple - unworthy of being used. So, on that last upgrade to Sequoia 15.1.1, SeaMonkley got bounced, and I could not get it to open.
Jason managed to get SeaMonkey back up and running, and I now have to open it through the Terminal and using two passwords, my email password and my computer password. I'm not sure Jason's instructions would have done you any good.