I think the answer may be to do one of two things:

1. If the database is on a mail server, sign it with an ID that has administrative rights on that server (as outlined in the "Using This Database" document) and uses that server as a home server.
   
   
   
2. OR -
   
   
   
3. Add the value AMgr_DisableMailLookup=1 to the server's Notes.ini file. Not sure if you have to restart the server (or Agent Manager) after you add the value or not.
   
   
   
   This suggestion is from a "Troubleshooting Agents" article by Julie Kadashevich (I copied the relevant text below). Please do tell me if it works or not – if so, I'll update the database documentation accordingly. If not, I'll try to think of something else.
   
   
   
   Thanks!
   
   
   
4. Julian
   
   
   
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   Troubleshooting agents in Notes/Domino 5 and 6
   
   by Julie Kadashevich
   
   http://www-128.ibm.com/developerworks/lotus/library/ls-Troubleshooting_agents_ND5_6/
   
   
   
   “After new mail has arrived" agents are designed to run on the home mail server of the agent owner (signer). If the agent is replicated from your home mail server to another system, or if you are trying to run an agent that was written by someone else, your home mail server will not match the server on which you are attempting to run the mail agent, and the agent will not run. You can suppress the check for the home mail server by adding the following setting to the server's Notes.ini file (supported in R4.5 and later):
   
   
   
   AMgr_DisableMailLookup = value
   
   
   
   where value can be 0 (check for the home mail server) or 1 (don't check for the home mail server). The default is 0.
   
   
   
   By suppressing the check that forces the agent to run only on the home server, you can have the agent run on multiple servers. Depending on the logic of your agent, allowing it to run on more than one server may cause replication conflicts and processing of the same logic more than once.