iphone and mac email syncing problems

I had a similar problem and eventually solved it.

Problem as follows. Three devices: MacBook, iMac, and iPhone. Apple Mail on iMac, and iPhone synced perfectly. Deleting or moving an email on one device would lead to the the same happening on the other devices. This was not so between my MacBook and the other two devices. In fact, I found that the problem was only with one account (my work email account; my home email account, Gmail, was fine). So on my MacBook I would delete or move emails in this account but things would stay unchanged on the iMac, and iPhone.

Solution. The solution was as follows. On the problematic device (MacBook in my case) do the following. (1) Quit Mail. (2.1) In System Prefs > Internet Accounts deselect the offending account (2.2) Open Mail (the account will not be there); (2.3) Quit Mail. (3) Go to Library > Mail > V9 > Mail Data and delete all files starting 'Envelope Index. (The folder might not be V9, it might be something similar, such as V7 or V11 perhaps.) (4) While still in Mail Data look at the folders with long strings of letters and numbers (e.g. AC7D8BA0-D3D5-4289-AF19-C42EC9U4BD94). Look inside these folders and you will see that they have subfolders corresponding to the mailboxes/folders in your email accounts. Use this to identify which of the folders with the long string is the one corresponding to the account with which you are having trouble. Delete that folder. (5) Go back to System Prefs > Internet Accounts and reselect the account. (6) Restart Mail.

You will now have to wait a while for Mail to import all the emails for that account from the server and to index them. That can take a long time, but it was worth it to me to solve the problem. I am not sure whether steps (2) and (5) are necessary. But I do think that step (4) is the key, since deleting this older forces Mail to re-import all the messages from the server, thereby re-establishing the right connections. (If you are cautious you will move rather than delete the files/folders in question.)

I hope this works for you.

My error, if it is type GMAIL then it should work. You can try deleting the account, restarting your phone, and adding it back. If that doesn’t fix it you need to try Google’s help, as the problem is with the account, not your phone.

Email never syncs device to device; it syncs to the mail server, so if there is a problem with mail not the same on different devices that means that one of them is not syncing correctly with the server.

Start by going to the mail settings on each platform and verify that the account type is not POP, as POP email does not sync both ways.

Who is the email provider for the account with the problem?

And what about going to Settings/Mail/Accounts, tapping on the account with the problem, and seeing if it says POP account or IMAP account?

No, they will still be there on the gmail server, and they will sync back when you reinstall the account.