Mail Uses All Available Memory Resulting In "Out Of Application Memory" Warning
This issue has persisted for a couple of years now and Apple does nothing to fix it. I've had the problem since at least macOS Ventura, continuing through Sequoia.
There is a simple fix: DON'T USE APPLE MAIL ON YOUR MAC!!!
Download and use SPARK from the App Store. You can access all your accounts in one place and it works without issue.
I've completely given up on Apple fixing this issue and you should to! Shame on them really!
MacBook Pro 16″, macOS 13.7