Step 1. Go to Sentbox, see which emails have a red delivery status. Hoover over the status to check why delivery din't succeed.
Or
Go to Exports. Download the Email History Export. Filter the exports on bounce = 1, check reason why mailing is bounced.
Often it's because of the spamfilter, in this case we strongly suggest to send an email again.
Step 2. Go to Attendees, search for the attendee(s) name(s), select them and click on the bulk action > Send
Step 3. Check status in Sentbox or exports. if it is delivered this time, no further action needs to be taken.
If not:
Step 4. Go to Sentbox > search for email and person you have to resend the email to.
Copy the whole email (which includes the personal link) and sent it via your own mailing system.
Remember: each email in the sentbox has its own magic link connected to the receiver (an email adres) You can NOT send one email to more people. You have to copy-paste per attendee his/her personal email from the sentbox.