In Skype for Business, a list of conversations was saved to the Conversation History folder in the Archives email box on Exchange Online by selecting Save IM conversations to the Conversation History folder in e-mail, as shown in the public information below.

Title: Find a previous conversation - Lync
URL: https://support.microsoft.com/en-us/office/d1d54123-0301-482e-b047-c82e9e2724a3

This conversation history was automatically saved as a trigger for screen lock, application termination, etc., and the history of conversations over a certain period of time was saved in chronological order with time stamps and display names, and shared files were saved as file links.

Outlook also provides search capabilities, which was very convenient.

Title: Find a previous Skype for Business conversation
URL: https://support.microsoft.com/en-us/office/18892eba-5f18-4281-8c87-fd48bd72e6a2

When this is achieved, the history searched by content search will also be more useful.
It is thought that it will be possible to solve the contents requested by the following feedback.

Title:Return a whole conversation when using Content Search in Security & Compliance
URL: https://office365.uservoice.com/forums/289138-office-365-security-compliance/suggestions/37536220

I want you to provide the same conversation history storage feature as Skype for Business.