ernst98 Said:
"Mail partly working: I just set up my new macbook air, my mail synchronized but it hasn’t downloaded everything. I receive new mail on my iPhone but my mail on mb says up to date but no mail coming in. Then when i check again my mail is on read only and empty mailboxes"
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Troubleshooting iPhone Mail:
A. New App Password:
Being this is a new device, note that you would need a new App Password, being that Mail is a third party app. You cannot log in using your eMail address password. As an example, go here for gmail: Sign in Using App Passwords - Gmail Help - Google Support
B. How Many eMails?:
Note that if you have thousands of eMails, that it will take some time for it all to sync. So, you'd just have to wait it out.