how to add an email account to my Mac

you just add it back as if it were a new account, all your old emails will be waiting for you.

IMAP mail protocol is set up for Multiple Readers (like your computer AND your phone) and all the emails are stored on the Server on the internet. When you want to read more than the email headers, the body and attachments are 'downloaded' to you to read. When you mark one as read, it is seen as read by all devices.

Follow the steps at > Add email accounts in Mail on Mac - Apple Support

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