Apple Mail, the OS bluetooth subsystem and some other applications (e.g. Fantastical) loose relevant (but not all) configuration and preferences on nearly every reboot. For Apple Mail it seems that all lost settings are stored in the file ~/Library/Containers/com.apple.mail/Data/Library/Preferences/com.apple.mail.plist. I haven't yet identified the other affected files.

What could cause the file contents to be lost on nearly every reboot? It does not happen if I hunt for it (keep rebooting), but only after using the Mac for a while.

I currently run macOS 10.15.6 on a MacBook Pro 16" with only a few popular Apps from the App Store plus Microsoft Office.

I am a long term Mac user. The bad behavior started approximately 2 years ago after an update to macOS High Sierra (I think). The Mac became more an more unusable because of this and other strange bugs (it also started to become extremely slow, so I had to reboot regularly, loosing all settings afterwards). Repairing and even installing the OS did not help. Therefore, I got a new Mac and installed everything from scratch (no restore from a backup) and installed only very little software on the system. However, the preferences still get lost on nearly every reboot!

  • What mac do you have and what version of the System are you running? i have an old iMac with High Sierra and I don't have that problem. And why are you rebooting your new computer? Do you have any 3rd party software. – Natsfan Jul 30 '20 at 15:57
  • I reboot only every now and then, for example to install new updates. Unfortunately macOS Catalina is not very stable on the Mac Book Pro 16" and crashes every now and then when you simply close the lid. I have two such Macs (one for private use, one for business) and both behave this way even though they run completely different software. – h2stein Jul 30 '20 at 16:25
  • Try a different Mail client like Outlook. While I generally don't like answers that say to try a different product, but in this case, I've tried to use Mail on and off for years and they've never been able to make it reliable. This is one of those cases to just abandon it because it's (Mail) is a lost cause. – Allan Jul 30 '20 at 16:42
  • Mail is the most prominent software to forget preferences, but more or less all apps are affected at times. Yesterday it was "Things". It greeted me as a new user and started the introduction again -- even though all projects and tasks were still being shown. – h2stein Jul 31 '20 at 7:14
  • Not the answer to this question, but for future victims brought here by searching for problems similar to mine: See telnetport25.com/2020/04/…; in particular, restoring /Users/<your logon>/Library/Accounts helped one of my many problems with Mail.app, when my main account on my main Mac (10.13) got zapped when I was trouble-shooting a problem similar to this on my sacrificial Mac, on which I am test-driving MacOS BS. – Flash Sheridan Mar 10 at 19:43

This is user level corruption or system level corruption in almost all cases. Sometimes it’s third party software, but that’s the hardest to trace, so focus on the easy steps first.

  1. get a backup
  2. Make a new user account and see if that user can maintain mail settings across reboots.

Based on that you’ll know if you need to address your user preferences, repair the disk, erase the disk and reinstall the os. After reinstalling, don’t set up the mac or restore the backup - just test the system with mail.

Then decide to wipe a second time and restore files / users or if you are better off setting up a clean system just transferring documents from the backup.

  • Thanks for the answer. I already tried the above steps: repair the disk, reinstall the OS, get a new machine and set-up everything fresh. Initially everything works fine, but after using the system for a while (weeks), things start to degrade. It is not practical to use a system purely for Mail (for weeks). – h2stein Jul 31 '20 at 7:11
  • That’s unfortunate @h2stein - your machine works as expected and then settings degrade? Do you think it’s just mail app or are other files getting corrupted? – bmike Jul 31 '20 at 11:59

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