If you're a Mac user who has been using Outlook for Mac (OLM) as your email client and you've decided to move to iCloud for your email and other Apple services, you'll need to import OLM to iCloud mailbox. This transition can seem challenging, but with the right steps and tools, it can be a smooth process.
In your Mac Outlook, click on File >> Import Mailboxes. Then choose Outlook for Mac from the given list and browse the OLM file that you want to import. Here you import OLM to Mac Outlook. After that configure your iCloud account to Mac Outlook. On the other hand, you can use the SysConverter for OLM tool and instantly import OLM to your iCloud account without any hassle.