[otrs] OTRS 2.2.5 Aget Interface email

Hello, We are looking to setup the E-Mail Agent Interface in OTRS 2.2.5, it works for agents, but as soon as a customer replies to a note sent from an agent either via the web ui or email, the customer gets a message from OTRS stating: "Sorry, AgentEmail rejected because no found!". The way this is curently configured, both the e-mail address customers send requests to and the address agents send commands to both go to the same account configured in the PostMaster POP3 Account in the admin section. Could this be the problem, or is there another posability? Thanks. Mike