Why don't you try a low-tech debugging aid

print @eml_id

print @rcpnt_cc

Just prior to the exec for the mail send and see of the addresses are OK. You could even cut them out and paste then into your mail client to see what happens when you try and send them.

If that provides no new leads then talk to your email admins and have them jump in with additional diagnostics message that are available to them that are provided by your SMTP server as well !