Apple Mail Rules Migration Mojave Hiccup

So that didn't quite work. I deleted those files on the new system, copied them from the old system, and when I looked at the signatures on the new system, it somehow still had the one test sig I had created earlier (and which should have been deleted) and nothing else. Almost as if there is a backup somewhere else in the directory.

But it gave me an idea: I looked at all of the files in MailData on the new machine, sorted by date, and deleted everything touched today.

Then I copied those same files from the old machine.

Seems to have worked like a charm!

So thanks for the suggestion and responses. You helped! I appreciate it.

Not sure what you mean exactly... To cover all bases:

I closed mail on both systems.

I then copied from the old and wrote it to the new system.

Once I had written the files to the new system and started Mail, it opened normally, no failures. Working like a charm.

I'm not sure if I got sidetracked before I posted my response earlier, so here it is again, but with an update.

I use SuperDuper! rather than Time Machine. However I'm creating a TimeMachine backup of my older system, and will then try to use it on the new system. A key question is will TimeMachine backups allow me to restore only the mail rules, and not the whole mail spool? And the update to my earlier response is that I just noticed my Mail Signatures didn't migrate either... So its now even more of a challenge (altough 40+ rules with up to 50 arguments in each is a really painful task if I have to redo it by hand :-().