Για να δείς το περιεχόμενο της ουράς μηνυμάτων
postqueue -p | more
the above commands display all queued messages (Not the message itself but the sender and recipients and ID), The ID is particularly useful if you want to inspect the message itself.
postcat -vq XXXXXXXXXX
View message (contents, header and body) in Postfix queue
Assuming the message has the ID XXXXXXX (you can see the ID form the QUEUE)