My "all mailboxes" has disappeared along with my opened emails

lynntg wrote:

Thanks again Leroy - working fine now, but still missing ten years of emails stored there.

Long term storage is usual in the "On My Mac" section...

Same thing holds true

if no insight or resolve the simplest is to restore from a recent backup.

If you see the mailboxes were you expect you can 'try' the rebuild feature:

if in doubt use the search window

If you value your user data

3-2-1 Backup Strategy: three copies of your data, two different methods, and one offsite. 

More than one device, more than one backup methodology.

restore items backed up with Time Machine

Restore items backed up with Time Machine on Mac - Apple Support

Restore your Mac from a backup

Restore your Mac from a backup - Apple Support

Rebuild mailboxes in Mail on Mac - Apple Support

lynntg wrote:

Thanks Leroy. I had done that but where are all my old emails? I leave opened emails in the inbox so I can refer to them later. Now they are all gone.

Well good question..

Old issue, new issue, what changed?

Have you shut down Mail.app, shut down and restarted your Mac..?

Have you tried the Mail>Window>Connection Doctor and verify your account is on line?

If it is a server issue it may be temporarily off line— try again later and compare your results.

ref:

Log out, sleep, wake, restart or shut down your Mac

—Shut down or restart your Mac - Apple Support

—Use Connection Doctor in Mail on Mac - Apple Support >Show Details

lynntg wrote:

How do I get it back & where are my emails?

Is it a matter of moving your mouse to the right side to reveal the + and the carrot drop down ?