On My Mac Mailbox folders gone on new MacBook Pro

GabbyGunner wrote:

I just got a new MacBook Pro running Sonoma 14.3. My previous MacBook Air died, but I had everything backed up to iCloud. I had most of my mail in folders saved "On My Mac". All my message have been downloaded to my new computer and when I search for a message I had saved in a folder "On My Mac" I can find it. However, all of the folders I had organizing these emails under "On my Mac" have disappeared. So the messages are on my computer someplace, just none of the folders. Any ideas on how I can get the folders back?

On My Mac, is just that, mailbox(s) you created & have stored on your Mac—not iCloud.

If you have Time Machine backup you can restore the V10 folder:

~/Library/Mail/V10

ref: Restore items backed up with Time Machine on Mac - Apple Support

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

GabbyGunner wrote:

I back up my entire computer to iCloud. I don't use Time Machine. So are you saying that iCloud backed up all my messages but not the folders I had them stored in?

I do not know how else to say it...

"On My Mac" is just that, mailbox(s) you created & have stored on your Mac—not iCloud.

If you value your user data

3-2-1 Backup Strategy: three copies of your data, two different methods, and one offsite. 

More than one device, more than one backup methodology.

—Back up your Mac  Use Time Machine to back up - Apple Support

ref: What does iCloud back up? - Apple Support