MDA docs

Welcome messages

Joins, leaves and boosts. All three are templates, so they take ${usermention}, ${servername}, ${membercount} and the rest.

Option What it does
Channel Where the public welcome goes
Direct message A private welcome, which survives them missing the channel
Delete after Remove the welcome after a number of seconds

Leaves usually want a staff channel rather than the one members read. Boosts have their own channel and wording.

Roles handed out on join are under Join & reaction roles.