Exchange SMTP Queues Growth Period

I have an Exchange 2003 Server where the “SMTP Queues Growth Period” in the “Tools – …Monitoring… – “Satuts” keeps growing after startup to 2000+ minutes. Emails are not sent anymore. Maybe only after a startup while the queue still didn’t grow.
Note that there are no stuck e-mails in the “Queues”, and when the server starts up, e-mils are sent. Only later, I don’t know after what SMTP queue minutes limit, e-mails are not sent out anymore. And it’s probably not virus issue sending mass mails.