Just to close this thread for others who may be reading it; this bug is not going to be fixed in 4.x releases , but has been fixed for 5.x. Therefore, if your admin address is not in the form admin@fqdn, you need to be aware that for every 4.x update you run from now until you upgrade to 5.x, you will need to fix your admin address following the upgrade. You can do this, as noted above, by running this command as Zimbra user:
Without running this command, you won't get your daily mail reports, and your log will have bounce errors for the reports it tried--and failed--to send.
zmlocalconfig -e firstname.lastname@example.org