App for starting threads/conversation with registered members?

[richardkmg]

Hello,

I'm building a store where registered members can communicate with me and upload files, and I can start a conversation/thread with any existing member as well. These threads/conversations will be saved and can be accessed whenever the member logs into their account on the website.

I'm guessing no app exists that can do both, so the solution may look like a combination of 2 apps:
App #1: registered members can open up multiple conversations/threads with me
App #2: I can open up multiple conversations/threads with registered members

Can anyone recommend apps that can help me do this?

Thanks.