Um, Liz, it's really better NOT to start new threads on the same issue. If you were having a different issue, then yes, by all means, but it gets very confusing if you have two threads going on exactly the same problem.
Anyway - do you happen to have a Time Machine (or cloned) backup?
Now would be the time to try rolling back to a spot when Mail was working - I'd try restoring your entire user->Library->Mail-V2 folder and see if that helps. And then replace the Mail preference files too. Then restart Mail and see if that works.
Another option - recreate your mail accounts in Thunderbird. It's free - you can download it here:
https://www.mozilla.org/en-US/thunderbird/The really nice thing about it is its setup - you really can see what it's asking, what you've put in and whether it's working properly or not. It's great for troubleshooting mail issues. I know - I spent hours doing it this morning when 5 Hostgator mail accounts on two different domains decided to stop working (it turns out it's an Apple/Hostgator issue of unknown origin - I'm not the only Hostgator customer with this problem and it's been kicked up a level for further study and no doubt, some conversations with Apple. Nothing to do with your issue...but Thunderbird was quite helpful, in proving that it wasn't MAIL per se, but rather an Apple-Hostgator issue, as it's happening on phones and iPads and also with older Mac OS', but not on Windows machines).
Also, Yahoo IMAP email is NOTORIOUS for issues - I had a horrible time with it for several weeks back in February. It was a Yahoo/Rogers issue, but it took them weeks to fix it (stuff wasn't syncing). Rogers, my ISP, uses Yahoo, and since we have Rogers here and at our summer place, I'm not about to abandon my primary email addy.
At this stage, if you cannot get Mail to work again, and you don't have a backup (you could restore the app itself from Time Machine too), you may want to consider reinstalling the OS. But make sure you have a backup in place before you do that.
First, starting a new thread came about because I thought I was changing the subject. I didn't start a new thread one time and got dressed down.
I do have Time Machine. I also have a exterior hard drive. It's been several since I did any backing up. I assume mail would be there only old.
There is a lot recommended here so where would be the best starting place?
You say,
QUOTE
I'd try restoring your entire user->Library->Mail-V2 folder
Do you have a link for instructions?
I'm not sure how
QUOTE
recreate your mail accounts in Thunderbird
works. Downloading it, I can do but how would Thunderbird recreate the mail app?
QUOTE
(you could restore the app itself from Time Machine too)
Do you have a link for explaining this? Or would you advise that I start with the least invasive thing and go from there? If there is any such thing.
Also, when I opened Mail in another users name, mail is all there, including all my folders, sending and receiving as ever. The only thing I see wrong is that it is formatted just like web mail. It's better than not having email at all, but the reason for working so hard for the mail app, as I've always known it to be, is the ease of use.
I'm afraid I'm now quite confused as to what you're doing/have done. Starting with your last statement - "I opened Mail in another users name, mail is all there, including all my folders, sending and receiving as ever...."
Um...do you mean you created another USER account in the System Preferences, logged in as this other user, and then put in all the settings for your Mail (Yahoo and me.com accounts) and everything works? The display is a preference - go to Mail->Preferences->Viewing, and change it to what I suspect was "Classic view"....
Anyway - if that's the case and Mail is working fine if you're logged in as a different user, then there is nothing wrong with the accounts themselves; you've got a corrupt file/preference somewhere.
Please let us know if that is in fact what you've done before we go any further.
As for the backup situation - there are words missing in what you typed, so I'm not sure when you last did a backup and therefore whether the backups would be of any use.