When someone enters a congress and gets their email wrong ( for example putting 2 ls in gmaill! ), or you try to send a mass email to previous congress entrants and their email does not work any more, then I get a mail delivery error sent to donotreply@congress.org.uk. But I don't have time to respond to all these. Possible solutions are - someone else volunteers to do something with these or we create a separate email forwarder for every congress to they get the email delivery errors, but then someone has to set up these forwarding rules and I need help with that. Also it might be possible to report errors to the organiser who is sending the mass email.
When sending mass emails it might be possible to detect failures due to invalid email addresses and report these back so that those people could be removed from the mailing list.