When the ACProcessAction agent runs it is run as a background agent and therefore looks in the Notes.ini for the location of the mail server. There must be an entry in the Notes.ini similar to this MailServer=CN=Your Server/O=Your Organization. Without this entry everything will work correctly but no mail will be sent. If the agent is run manually by a user with the role [ACAdmin] and Manager rights to the database mail will be sent because Notes is using the settings in the current Location Document. Newer installs of the Domino Server automatically include the MailServer= line in the Notes.ini but we frequently find that it is missing from established Domino Servers. This only impacts background agents that send mail so is frequently not identified until a product like Workflo!Approval is added to the server.