There is a very good article on Ms TechNet concerning this very task - Works well and isn't too difficult.
https://gallery.technet.microsoft.com/office/olm-file-to-apple-mail-b5835cdb
To import PST files into Apple Mail, you have to convert the files. There are a plethora of converter programs on the Net, many are listed and reviewed for good performance: (I did not find any of them to be free) http://pstconverterpro.com/migrate_outlook_pst_files_to_apple_mail.html
You can go directly to the folder where Mail saves its data through the Finder and duplicate it to store a copy elsewhere. Inside the Finder, menu Go > Go to Folder and then paste this path:
~/Library/Mail/V5
It is that V5 folder you'd want to back up before reseting Mail. There is also some...
This topic has been discussed multiple times on various forums and now it's pretty clear that you cannot directly export and import your emails from apple mail to outlook mac. I think that apple and microsoft should work together and provide some kind of way to this situation. However, there are...
It's better if you allow the export function take its time. Your database might be heavy, hence the time is being taken. For manual methods, the export function is the only way to backup your outlook mac.
However, there are other alternatives also...
If you want to convert Mac OLM file data to PST format, I would suggest you can try an easy manual trick that can effectively repair or restore your corrupted OLM file to Outlook PST files.
First, you create an IMAP mail account, then configure IMAP mail account to Outlook Mac. Create a Gmail...
There is another third party tool that is gaining popularity because of its multiple features for email backup solutions for all the email clients in mac. Its Mail Backup X, you can have a look at its features here: http://www.mailbackupx.com/
Best solution is to export your email database, that way your emails also remain safe and secure. Here's the procedure:
Export mailboxes
Select one or more mailboxes, then choose Mailbox > Export Mailbox.
Choose a folder or create a new folder, then click Choose.
Mail exports the mailboxes...