3pid invites are sent referencing room id, not alias

[matrixbot]

Created by @ matthew:matrix.org.

Therefore if the recipient signs up with their own HS, they won't be able to find the room they're invited to, unless we do the heuristic of querying the server from the room ID's domain

[dbkr]

A lot of the time you'll be inviting people to rooms without aliases though, in which case this won't help.

[dbkr]

We should be able to add via parameters to fix this now - I'm not sure that we do for 3pid invites though

[t3chguy]

Also if the alias were to be re-assigned it'd nuke the 3pid invite