Old “On My Computer” emails stuck in Legacy Outlook, and Apple Mail is toxic and incompatible with Gmail.

Next month, Legacy Outlook may rapidly become unstable and unsafe because Microsoft will stop supporting it. I use Gmail as my server and have an active Gmail mailbox in Legacy Outlook. But I also have a large old "On My Computer" mailbox, where I file emails I need to keep.

The reason I do this is that "On My Computer" mailboxes are static and cannot be messed up by sync errors, IMAP incompatibility, or the like. As you may be aware, if you have a Mac and try to use Apple Mail to manage Gmail, your entire active Gmail directory system can be collapsed and all structure lost.

If you have an old "On My Computer" mailbox, you may also have noticed that when you switch to New Outlook, that old mailbox is not imported successfully.

In my case, I had an "On My Computer" mailbox that had a few hundred emails in nested subfolders. It had been launched in 2002, and so there was a lot of corruption mixed into the source code.

I attempted to export the mailbox using Outlook to create a .pst file, but New Outlook cannot import those. I tried using Gladwev and OLM Converter but both failed, presumably due to the age and corrupted nature of the source "On My Computer" mailbox. I thought about installing Thunderbird and using it to do the importing, but I was concerned about wasting more time, and, a friend who's much more in-the-know than I am told me that he was skeptical about Thunderbird's long-term fate. His advice was to abandon Microsoft and just use Google's native web interface for Gmail. I don't love that interface, but I did feel that it was necessary to get all of my old emails out of that "On My Computer" folder into an active mail system of some kind, so that I could search within them and reply to old threads as needed.

I figured out a simple solution that does not require any third-party software. The end result is that my entire old "On My Computer" directory is now available in Gmail through its web interface, and, I have a robust searchable backup.

1. I gave each subfolder a numerical prefix so that they'd sort logically.
2. To be safe, I converted the directory into a flat structure, meaning no subfolders.
3. For each folder, I composed a new email and included all of the folder's contents (a bunch of old emails) as attachments to the new email. The result of this was that each old email (automatically) took the form of a .eml file attached to the new email.
4. I selected all of those attachments and dragged them into a folder named according to the numerical prefix and text name of the source mail folder (from the old "On My Computer" mailbox). The result was a folder in Mac OS's finder, containing one .eml file for each old email. Each parent folder or subfolder of the old "On My Computer" mailbox had now become a folder in Mac OS's finder, and it contained one .eml file for each old email that had been in the Outlook mailbox.
5. I then went to Gmail's web interface and created new folders with the same name as each of those folders. (This step works in New or Legacy Outlook too but I was mistrustful so I did it directly in Gmail on the web.)
6. I then opened New Outlook (simply by de-selecting Legacy Outlook from the Outlook drop-down menu at the left of Outlook's menu bar). All of my newly-created Gmail labels now appeared as Outlook folders within my active Gmail Inbox master folder.
7. For each of these Outlook folders, I simply dragged all of the .eml files in. They were automatically converted into emails. So now every email that was in a parent folder or subfolder in an "On My Computer" folder in Legacy Outlook is now in its own folder in New Outlook's Inbox for my Gmail account, and every one of those emails is appropriately situated in the correct label in Gmail's web interface.

It really sucked that I had to do this and it's unbelievable that no reliable solution exists that could have accomplished this without so much manual labor. But my experience with the failure of Gladwev and its sister program led me to favor a manual approach over further attempts to get it done automatically…and I certainly did not want to follow Gemini's suggestion and write Python code to be run in Terminal.

So there you have it. Quite a pain but kind of a lifesaver. The whole thing took less than 2 hours, if you don't count the 5 hours I spent trying to get it done "automatically." Just so you know, you can also select a large number of emails in Outlook for Mac and click Print and then Save As PDF, and a single large PDF will be generated from all of those selected emails. That will preserve their content but will still leave you having to copy and paste email addresses and old content whenever you have to reply to a thread.

I hope this helps a few people out there…good luck and welcome to the modern age of full-bore enshitification.