Getting the best out of OneAll (social signin) - how?
Installation and Configuration
right now there is no built in functionality that sends out a "Welcome" email. You could use the Newsletter system with a filter of when they logged in, but that would mean doing it each time someone signs up. Maybe the "Email Course" module could do it for you.
The intention of that module is to send out periodic emails based on an event at X days interval after the event.
Marketplace: Email Course
https://www.jamroom.net/the-jamroom-network/networkmarket/604/email-course
I haven't used it in a while but think it was configurable to start when someone signs up.