Mail rules erased each time Mail.app starts
This is an old problem that has not been resolved.
For me it just started after I installed the latest IOS update 916.6) on my iPhone.
Mail rule are located in ~/Library/Mail/V10/MailData/SyncedRules.plist.
I also have a V2 and V6 folder, but read on.
After my rules disappeared, I copied SyncedRules.plist from Time Machine and replaced the new one.
No joy.
Mail overwrote it when I restarted it.
Thinking that it might have had something to do with the file creation date, I copy/pasted the contents of the old file into the new.
No joy.
Same thing happened.
NOTE: The same plist exists in both V2 and V10, but they are not changed.
TIP: Here is an easy way of telling if a file has changed; tag it.
Tagging a file will put a colored dot beside it.
If the file is updated by the system, the dot will go away.
Theory: I have some rules set up via the iCloud online version of Mail.
Those rules are not affected by this BUG.
Maybe iCloud is erasing my local rules?
Are you listening Apple?
My next step will be to erase the iCloud rules and see what happens.
My guess is that this is not a bug, but moreover, a concerted effort by Apple to drive customers toward using iCloud more.
Stay tuned.
Mac Pro