I closed the email window and now it won't come back on the screen.

If Mail is still open, choose "Message Viewer" from the Windows menu, or press command 0 (zero).

You have not said what you tried to rectify the problem, so....

1. Quit Mail.
2. Open Mail. Did that work?
3. If not, quit Mail & Restart the Mac
4. Open Mail. Did that work?
5. If not, open Disk Utility.
6. Run ** First Aid on all internal volumes. The Data volume can take forever depending on the age of your Mac.
7. Restart the Mac and then Mail. Did that work?

Come back here to report the results, please. Let us know what worked or didn't work.

Do you have more than one Desktop? Check by pressing the F3 key or by opening Mission Control.

modelamac wrote:

Come back here to report the results, please. Let us know what worked or didn't work.

Not to jump to conclusions but, i believe my suggestion fixed it.