I have tried to invite people who do not have a Zoho account to a group I created, but they did not receive any invitation.

When I removed the two addresses from the group and readded them they received an email about being unsubscribed.  As a moderator I received a copy of these emails. I have not received a copy of the subscription invitation, though, so I think they may not have been sent out at all.

How can I check that the invitation email / subscription notification was really sent out?

Best,
Ricardo

PS: I'm very satisfied with Zoho mail.  Thank you for the great work!