you can assign up to 20 address lists to a single offline address book (OAB). The maximum size of a single offline address book is 1 GB.
The maximum number of contacts that can be added to a personal distribution list in the Microsoft Outlook Address Book is approximately 60~120. There is no maximum number of specific contacts because the actual limit is measured in kilobytes, not the number
of contacts. Exchange has an 8-KB limit on the contacts that can be processed.
More details https://learn.microsoft.com/en-us/office365/servicedescriptions/exchange-online-service-description/exchange-online-limits
Hope this solves your query!!
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