Mail does not open after Catalina upgrade.

Good news, it’s fixed. First, thank you to all who gave suggestions. I discovered the solution from a response to a similar problem posted back in 2014. Apple discussions.apple.com/thread/5957899. Help! Mail crashing with new OSX 10.9.2 update. I found my solution going to folder V7 rather than V2 as suggested in the blog. Here is the solution from Linc Davis: 

Quit Mail. Force quit if necessary.

Back up all data. That means you know you can restore the Mail database, no matter what happens.

Triple-click anywhere in the line below on this page to select it:

~/Library/Mail/V2/MailData

Copy the selected text to the Clipboard by pressing the key combination command-C. In the Finder, select

Go ▹ Go to Folder

from the menu bar. Paste into the box that opens (command-V), then press return.

A folder window will open. Inside it there should be files with names as follows:

·       Envelope Index

·       ExternalUpdates.storedata

Move those files to the Desktop, leaving the window open. Other files in the folder may have longer names that begin as above. Move those files, if any, to the Trash.

Log out and log back in. Relaunch Mail. It should prompt you to re-import your messages. You may get a warning that the index is damaged and that Mail has to quit. Click OK. Typically, the process takes a few minutes, but it may take hours if you have gigantic mailboxes. In that case, you may be able to speed things up by temporarily adding your home folder to the Privacy list in the Spotlight preference pane. Remove it when Mail has finished importing.

Test. If Mail now works as expected, you can delete the files you moved to the Desktop. Otherwise, post your results.

Hi Jameson.h,

Thank you so much for your suggestions. I have good news and bad. The bad news is that all the original suggestions ie: Restart, opening Mail while holding the shift key and Safe Mode had no effect. Good news is that making a second user does work. The mail program does open. What do you suggest next?

Thank you for your suggestions. The Mail version is 13.0 and I believe it is the latest version since it was crested on September 27th, the day I upgraded to Catalina. I cannot modify the accounts because Mail will not open.

Apple support suggested that I reload using the MacOS Recovery system (Command-R). Sadly to say it did not correct the problem. I did notice a progress bar and a message that flash very quickly before the Mail program crashed. It read "Upgrading your Mail database". Is this helpfull?

I will try Apple Support again but it appears they cannot help me, well at least the tech I talked to had no idea what to do.