Mail doesn't work with Sonoma 14.0

Are there Other Applications performing the same ways as Mail ?

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.

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

After the above testing and still an issue - post back if you would

Follow previous advise - First

As an adjunct

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.

I understand the frustration you're facing with Mail on Sonoma 14.0. I recently encountered a similar issue but it was solved after I updaterd my Mac to macOS Sonoma 14.1.1.

See if that helps fix the issue or not. In case, if you still encounter the issue, then you can follow this guide to fix Mail Doesn't work with Sonoma.

Feel free to reach out if you have any questions or need further assistance. Best wishes for a swift resolution!

Not sure if this is the issue (although once I made this change, my issues with Mail and Messages "seemed" to have gone away ... time will tell), but I disabled Sidecar (I didn't realize I had it enabled ... perhaps it's a default ?) and I don't seem to have any delays in Mail and Messages (which I was also having an issue with) seems to work.

Upon reflection, I *did* try using Sidecar a long time ago (in a previous iteration of the OS) but since then I no longer use my iPad (and thus don't need it as a second screen). Perhaps it's "hunting" for that other screen (and thus causing delays which manifest in more visible ways such as my Mail app).

Something for others to try

Also I find MANY MANY Mac OS users in Mail NEVER look at Mail's menu item 'Window' and select 'Connection Doctor'! It will show you the severe reply when using tithe button for 'More Info' in Doctor.app!

Did you try updating your Mac? The latest version released by Apple should fix this issue. If you have already done that but the issue isn't solved then you can follow this guide to fix Mail doesn't work with Sonoma issue.

I've had similar issues since upgrading. I did a clean re-install of Sonoma coupled with a Time Machine backup, still the same issues. What I've noticed is that I also have a "stall" in Messages (not just Mail). My *guess* (after watching Mail hang for a bit while typing in an email address into the "To:" line, is that there is something going wrong internally (either within my OS or perhaps iCloud) when either of these apps are resolving names (for instance in Mail, it's trying to auto-complete a known email address ... hangs for a bit ... then pulls up the list of possible addresses). Seen the equivalent happen in Messages. Still working on tracking this down but just in case it causes a light bulb to go off in someones head, posting this ...

I have Sonoma version 14.1.1 (23B81) and the problem with the MAIL application still exists, especially when starting it for the first time, the entire application hangs or when creating a message, it is sometimes necessary to turn off the entire computer. But surprisingly it happens from time to time

14.2 (23C64) Sonoma = despite the new update, the program hangs when you run it for the first time, you need to reset the application a few times and then it will start. At the moment when the application freezes, the temperature increases to 95 degrees on my Air M1 2020 within a few seconds. After several computer restarts, sometimes the symptom disappears. is this some kind of joke? Need to reinstall the system again???

Welcome

To Bad it required moving back to Ventura in-order to accommodate this Third Party Software.

Shame on the developers for not doing extensive Testing of their Software on Sonoma

The way I understand this, Apple does not build their Operating Systems to work with Third Party Software but rather the opposite

But if it works for your needs - good it works now.

The only issue I have been having with Mail in Sonoma was the communications between Mail and iCloud Mail Account.

It was often taking the account Off Line for no apparent reason

After the issue was moved up the Ladder to Level 2 Engineers, in a matter of 1 to 1 1/2 days - no more issues and No .1 update to Sonoma required