As you are looking for the best software to import Mac OLM to Gmail account then in my opinion, you can use KDETools OLM to Gmail Importer. User can use the batch conversion function to convert a single file and a batch file. This software provides so many advance and unique feature "split option" so that users can easily split the oversized files into small files with this feature.
OLM to Email migrate device is an email data transfer tool that instantly changes PST, EML, MSG., and MBOX format. Mail Importer Software supports the unique formatting, resources, and information of Mac OLM emails in the new database.
1. The tool migrates OLM to Gmail, G Suite, Google Drive and etc.
2. The tool preserves OLM items such as emails, contacts, calendar. folder, sub-folder, notes, journals, and etc.
3. The tool also supports email servers like Office 365 and Exchange Server accounts.