After having had Mail sync problems on my stock S7 Samsung, bought from /e/, running Android Nougat 7.1.2 and just updated to system 0.13, I want to share my email sync settings.
I could not find a suitable and complete answer elsewhere on this forum.
Note: menu names may not be accurate as I am on a French language /e/.
Here you are, Sync must be activated at all 4 levels (!):
1. Mail app
mail app > “…” menu (top right) > settings > account settings > email retrieval (or collection?) > email syncro > set at “all dates” (or your choice).
2. Phone parameters
Phone parameters menu (swipe down from the top of the screen), Syncro icon must be activated. If you cannot see the Syncro icon, you can add it by clicking on the pen icon at top.
3. Phone settings
Phone > settings > accounts > /e/ > myemail@e.email > “Accounts management” (“Gestion des comptes” in my French screen) > a popup propose to force sync. I accept > I am warned that forcing sync may reduce battery life. I accept.
(This last setting seems to have the same action as @Manoj proposed here but that do not work on my phone as Mail app is listed as “not optimized” and “Battery optimization not available”)
I just adjusted the Phone settings on my phone and it seems to sync OK.
But after restarting the phone, no sync again.
4. Open Mail app at launch
So, this is the 4th level: you must start the Mail app once for Sync to work (you can close it afterward).
You should be able to set Mail app to start at launch:
Phone > Settings > Privacy > Privacy Guard > click on the 3 dots at the top right > Advanced > swipe from the right to the left until the “RUN IN BACKGROUND” or the “BOOTUP” tab to directly see which apps are using those permissions (from here) > click on Mail app.
Hopefully, this should open a menu where you may activate launch at start.
Sadly, this last step brings me to an empty menu saying only “no available authorization to block”.
If all this can help someone. Great!
If someone can help me unlock that launch of Mail app at background, it would be great.
Note: I think that all this is not desired. Once the syncro in the Mail app is set, it should work right away or warn users that other parameters adjustments are required.