Have you checked the server that this agent runs on by opening the mail file in designer, looking at the agent properties and verifying the server name is correct in the target.
The Out of Office message will only be sent to an address once.
This list is cleared when the agent is disabled.
Therefore, disable then enable the OOF agent and try again.
Check the Schedule as discussed before for how often it runs. I have found that standard Notes 6 template set it to every 6HRS, which is pretty useless.
Also, on the server it is set to run type
Tell AMgr Sched
This will list the scheduled agents with the times they will be acted upon. Check for the mailfile path of the database concerned.
Other checks would be to look at the Agent Interval settings in the Notes.ini - Check Admin Help - Improving Agent Manager performance.
NOTE: Known issue with servers that have been running for over 100days. Mail-triggered agents run with no error, but no mail is generated. To fix, restart Server box at NT level not just Domino.