ma1uta
Multiple user invitations with email uses email "to: instead of "bcc"
Inviting people in a room with email ( sending multiple invites with one click ) during email invitation all emails that has been invited to join room show into to: which creates some "problem" because somebody can copy and paste this emails later somewhere else for spam or whatever reason.
Solution: When there is only one email invite use to: when there are more than two then put email recipients into BCC or known as blind carbon copy.
I cannot reproduce this issue or haven't understood it. https://matrix.org/docs/spec/identity_service/r0.3.0#post-matrix-identity-v2-store-invite accepts only an one email per request therefore if you invite 10 users via email then there will be 10 requests and ma1sd sends 10 emails with different to:, ma1sd won't union email into one.
I have tried to invite multiple users each one with their email ( system invited them automatically when you created a room ) but instead of emails to go in BCC to keep privacy who is invited in room ( at least to not copy their emails ) everything was going into TO: so all emails show there.