My Mac book air not receiving emails
wifi working emails not coming in
MacBook Air 13″, macOS 10.14
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The typical cure for this is to delete the email account in the Apple Mail app, then reinstall it.
This Apple Support article should help: Log out of or remove email accounts in Mail on Mac - Apple Support
Once you've deleted the account as per the instructions above, then reinstall it: Add email accounts in Mail on Mac - Apple Support
Hope this helps.