mac mail downloaded and removed all email from third party server
I set up my new MacBook Air by using a Time Machine backup from my old iMac, but when I opened the mail app on my MacBook, it downloaded all the email from my third party provider, and deleted all the messages from that server. Previously it was set to sync across devices. Now, all the messages that were on my phone are gone because they were removed from the server. I can't figure out how to stop the download and delete from server, nor how to restore the missing messages on my phone.
Any help is appreciated. thank you!
MacBook Air 13″, macOS 10.15