Mail Server A is trying to contact Mail Server B behind a firewall. Mail Server A makes the initial connection, but there is a consistent long delay (1 minute) before the queued mail is actually sent.
A reason for this might be:
A.
Mail Server A does not have a default route.
B.
Mail Server B does not have a default route
C.
The firewall is blocking TCP port 113.
D.
A third Mail Server is delaying the traffic.