If by sysxmitqueue you mean sys.transmission_queue then this will contain
Service Broker messages that can't be delivered.  The most likely reason for
them being undeliverable is that either Service Broker is disabled in the
target database or the target queue is disabled.  Try this for the
databases:

select Name, is_broker_enabled from sys.databases

and this in the target database:

select name, is_receive_enabled from sys.service_queues

Another possibility is that they are being sent to a service that doesn't
exist.  Service Names are case sensitive.

A good question to ask when you figure it out would be how did 7 million
messages fail to get delivered and nobody noticed?