No Ticket Update Mail notifications


we are using RT 4.4.3-2 and we have some queues that have an email address so if a mail is sent to that address a new ticket will be created and we receive a mail with the info of the ticket creation.
We also receive mail notifications if a new mail is sent to a existing ticket.
There are some other companies that also use RT and if they send a message from their RT to our RT it recognises the ticket id of the other companies RT and puts it in the subject.
The problem is in that case when our RT recognises that the message is sent from a other RT system we dont get mail notifications.
Thats a problem for us because we dont notice then that there already is a status update in the ticket.
Does anyone know how we can enable mail notifications for tickets where we are in contact with other companies that use RT?

Thank you in advance for any hints!


Does the RT sending emails into your RT have an email that matches your

Config? What do you see in the logs when you receive an email?