Mac Mail migration - no subject, no sender, no context

Mimi-Mac-2 wrote:

I would like to migrate data, including Mac Mail e-mail from my old Mac (Big Sur version11.6.4) to my new Mac (Monterey version 12.3.1). Mac Migration Assistant was used to transfer the old data from Time Machine. For the first attempt, majority of e-mail in new Mac were not imported, and no folder divisions (never mind).

After that, I tried to copy several files under Library/Mail/*.mbox (via Time Machine and network) and import them by Mail. Only a few e-mail were imported, and imported e-mail have ‘no sender, no subject and blank context’

Tried to use ‘rebuild’ option of that folder, and restart Mac, but these did not solve the issue.

How could I migrate e-mail?

Thank you for your help

https://discussions.apple.com/content/attachment/351977d8-105f-4fb3-9a37-42c709060f2f

For problem accounts remove the account and add it back in—

Remove email accounts in Mail on Mac

Remove email accounts in Mail on Mac - Apple Support

Add email accounts in Mail on Mac - Apple Support

Add email accounts in Mail on Mac - Apple Support

Note—

• IMAP accounts stay on the server, so no local loss, when you re-sync

• POP accounts download and remove from the server—therefor save your inbox/sent box if you want them

• "On My Mac" is just that, local folders you created and moved mail into. So no loss