A customer recently ran into an issue with a "missing" ticket, the overview sidebar claimed an inbox had one extra ticket than was showing in the ticket list. A search in the GUI would also not reveal this ticket. It turns out the missing ticket did not contain a reply address. This was caused by the customer temporarily removing (and forgetting he had done so while testing) the default reply to address configured in 'helpdesk setup'.
To hopefully prevent "false alarms" like this in the future it would be nice to convey that you cannot leave this field blank. If they don't want to use the default address they can always override it with a group specific address. We just want to at least warn customers that you shouldn't remove the default even for testing purposes.
Steps:
1) Click into 'helpdesk setup', then the 'Mail Setup' tab.
2) Scroll down to the "Default Preferences" section and delete the "By default, reply to mail as:" address (that was created during setup)
3) Save changes
Result:
Observe that there is no warning of any kind that this could have unforeseen side effects.
Bug
Open
[Helpdesk Setup] Warning that you must have a default helpdesk address to reply from