High Sierra - Mail Issue

Most likely it's just not toggled open.

Do you see "On My Mac"? If yes, hover over and select Show.

If you don't see, it's possible the "On My Mac" folders were not imported properly. What version macOS were you running prior to upgrading your Mac? do you have a Time Machine backup?

In your User's Library/Mail folder, do you see other folders named V2, V3, V4?

I suspect we might need to do a complete reset of your Mail folder.

Quit Mail.

In your User's Library:

1. Rename the Mail folder to MailXXX

2. In Containers, delete com.apple.mail

In System Preferences > Internet Accounts

Uncheck Mail for each account.

Restart your Mac.

System Preferences > Internet Accounts, check Mail for only one IMAP account. We can add other accounts once we get your "On My Mac" data imported.

Open Mail.

Look in your User's Library/Mail folder to see if it setup up with new folders.

You should see two alphanumeric folders. One will have the Outbox. This is the "On My Mac" folder. The other would be your IMAP account you added.

In Mail do you see "On My Mac" in the folder list?

If yes, let's import your "On My Mac" folders. We have two options.

1) Use Time Machine

2) Select to import from the Mailxxx folder

Let me know which option then I'll give you specific instructions to import.

Ok, do you want me do delete the following files too?

com.apple.MailCacheDelete

com.apple.MailServiceAgent

Yes, let's delete those as well.

To import from the Mailxxx folder you first need to identify the correct alphanumeric folder with your "On My Mac" files. Once you have identified the correct folder, in Mail, under File > Import Mailboxes... select Apple Mail > Continue. Navigate to the Mailxxx folder and select the correct folder to import. Occasionally they will import weirdly. Let me know so we can try a different option.

Let me know how it goes.

Are your folders named correctly and not showing as numbers etc? If yes, glad we have finally solved your issue.

If you had lots of signatures we can bring those over or you can create new sigs using your Sent messages to copy your old sigs.

You had Bundles. these are for third party add-ons like SpamSieve, MailTags, Mail Add-on etc. You'll need to add back by reinstalling.

You can delete the Mailxxx folder when you are satisfied with the new setup.

Have you tried any of the suggestions?

Generally, it's best to start your own post. Suggestions are often specific to an individual and when mixing in the same thread it can get confusing.

Try to make a more specific subject for your question. “Mail Issue” is so general, users searching for an answer for "why don't I see my "On My Mac" folders" might not find this discussion.

Thanks for the reply. Will start a new in future, however.

Worked all the way, I had the exact same issue hence the ask. Only concern was missing rules, sorted by re enabling when the penny dropped.

However the long hex numbered folders appeared but I have dealt with them by moving the mails contained to my main "on my mac" and will delete them once I get them sorted (I backed up the xxx named folder anyway).

Think I am OK now.

If I may ask, I have the same issue. Is this OK to piggy back on here?

I see you got hit with the "Occasionally they will import weirdly" issue. There are other ways around this, but seems you got it all sorted manually.