Similar results with new Gmail account. Can't verify via Safari (won't launch). Generating App password via Google App does not work either.
Yes, I facing exact issue on other IMAP provider, iCloud and gmail works just work fine. Already try to rebuild, restore and even to the extend to delete all the login like a fresh Apple Mail. Nothing helps. It’s just don’t show up, but if you search for email and it’s will appear then and go off after that. Also try this step too, nothing works. www.systoolsgroup.com/updates/fix-apple-mail-emails-disappear-from-inbox-error/amp/
Telstra IMAP account refuses to retrieve new mail.
The problem persists with macOS Version 10.15 Beta (19A512f).
I can compose and send, but Mail refuses to see or retrieve new mail to Mail InBox from my Telstra (Bigpond Australia) Accounts.
iCloud, Hover, Hotmail, and Gmail accounts, all IMAP, are behaving as they should.
So does Mail on my iPhone 7, with Telstra Account...
A new Telstra Mail account (rather than my prime account) also misbehaves.
Mail in macOS Mojave (running from a Clone on an external SSD) behaves as it should, retrieving all mail from the Telstra accounts.
The issue clearly relates to Catalina Mail App.
I am having issues too. Installed Catalina on fresh hard drive. Used TM to bring in Mojave data. 5 mailboxes all appeared OK, but one showed subject lines, but no body text. Any fresh ideas out there?