From Office 365 admin center i created a new MS Teams, which have created a new Office 365 group + SharePoint Modern Team site. Also when i added members to the Office 365 group, the new MS Teams appeared inside the users' Teams desktop application.
Now there are 2 ways to add conversations to the MS Teams:-
1. using the desktop application as follow:-
2. OR using the Conversation inside the sharepoint team sites >> which will actually open the users' outlook, as follow:-
So my question is what are the differences between adding the conversation using outlook or using desktop application, as adding conversation using one method will not show it inside the other, for example i added a conversation using the desktop application, but it did not show inside the users' outlook accounts, while it showed inside the users' desktop applications....
Chats are actually stored in Azure as Juan pointed out. However, if you have Exchange Online on your account, and I think on newer On-Prem exchange works, but copies of all these chats get saved to your inboxes in a hidden folder similar to conversation history from skype for business that is accessible via Content searches.
Team channel conversations are stored in azure and copied to the same folder on the attached group mailbox (hidden) similar to chats.
Files in chats get saved to the uploaders or chat starter's MIcrosoft Teams Chat Files (Upload) or inplace share from OneDrive.
Files in Teams are stored in default documents library in attached SharePoint site.
The Outlook link is to the Office 365 group inbox which is basically a shared e-mail inbox with group membership.