cannot delete blank email in apple mail

Very recently, when I experienced the same problem for the first time (a blank email on screen that I could not delete, even by restarting my computer), I phoned Apple for help. The agent helped me get rid of the blank email by doing this.

First close Apple Mail. Then, while holding the Shift key, reopen Apple Mail. The Apple representative told me that doing that clears the cache in Apple Mail and some other applications.

This has worked twice for me, but it never used to happen. My version of Apple Mail is 16.0. Perhaps it is a bug in macOS Sonoma (my version is 14.3.1).

Jan

5 - There could be something in the main User Account playing up.

To further isolate this - Set up users, guests, and groups on Mac.

Then log out of the Main User account and log into the dummy account and test again if the issue persists.

6 - If the issue is present in the dummy account - then, this appears to be a System Wide issue on the computer.

7 - Download the Application Etrecheck directly from the Developer.

This is a Diagnostic Tool that makes no changes to the computer.

It makes a coherent and readable inventory of both the Hardware and Software used on the computer 

The application is free or paid from added features. 

The Report will Not Reveal Any Personal Information. 

Post back the Full Report - copy and paste - >>>> using the Additional Text Icon ( 3rd Icon to last ) <<<<

Once done, then a collective We, as in those participating in your question, can have a look and see what may or may not be a cause of this issue

Does the Window menu -> Activity menu item indicate any unfinished email checks?

If not, rebuild the Spotlight index.

Rebuild the Spotlight index on your Mac - Apple Support

1 - Restart in Safe Mode. This will perform a Disk Repair, clear cache files and only load Apple Software, extensions and fonts. The boot up will be slow and can take some time - Normal.

2 - Safe Mode will also eliminate Third Party Software, extensions and drivers from loading. It will only load the Minimum amount of Core Apple Processes to allow the the computer to function at a reduced Level of Performance 

3 - Does the issue present in this mode ?

4 - Sometimes a Safe Boot followed by a Normal Boot will just put things right.

5 - If Not already installed ? >>>

Links below

Keep your Mac up to date

About the security content of macOS Ventura 13.6

About the security content of Safari 17

Is this a e-mail you received that is Blank and cannot close ?

If so, " Take ALL the Account Off Line "

Then, try to Close the window

Hello pottipete,

These blank windows are due to an e-mail stuck in one of your outboxes. Deleting the e-mail will fix the issue.

Welcome

In regards to the Etrecheck Application and some context for future usages should it maybe suggested.

At one time there was an  Etrecheck Application available on the Apple Apps Store.

Due to certain constrains place upon the Developer by APPLE, the developer chose to remove it from the Store and make is available Directly from them.

This specific application is well known, on these Forums,  as a Go To for trouble shoot and avoiding all the question / answer and question / answer to finally get the issue pinned down.

It is also known and reported by Reliable Sources that,  sometimes APPLE SUPPORT has invoked using this same Developer Distributed Version of Etrecheck application to trouble shot computer issues 

If you do a quick search on the Front Page of there Forums using "  Etrecheck " you may find about 287 Posting related to the usage of this application

Lastly - should you decide to use and post the Report now or at a later time, we are willing to have a very close look and offer some insights 

PS - I am not affiliated with nor do I receive any compensation from the Developer for suggesting or using this application - Incase that may also be a concern you have 

I too am a happy user of Etrecheck. So if you ever run into technical difficulties that other support professionals can't solve, you can use that report on this support communities, and many of us volunteer techs can help you identify the issue. Glad to hear that Apple found the reason of your stuck email.