[otrs] Unable to respond via email

Hi there.. New user to OTRS - have the system up and running... I know I'm missing something obvious here, and after reading the docs must have missed something ;) Have setup a queue and can get a test email to showup in the system but cannot respond via email. The queue has a proper email address associated to it, but only option to respond is via phone. What am I missing? Best regards, Paul Stewart