Not yet possible regarding their known issues in v0.1.
Inbox and search are incomplete Unable to comment or create posts Some comments are displayed in the incorrect position Comments aren’t visible on user profiles Posts aren’t marked as read when viewing an image Unable to upvote comments
I use my own domain in iCloud since 6 month or so and it works with no issue. After setting up in iCloud you can turn on/off the „catch all“ option.