From Verizon support:
The 6250 message is a wake up message for the Sync & Connect email component of the Backup Assistant Plus (BUA+) service available on the device. If the device is capable and has the BUA+ client it should understand the 6250 message as the email alert update on the device and not display it as an unintelligible message. We are looking for reasons why the client may corrupt and display it as text. If the email end points are removed from the web
(steps here)(see number 10 and 22) and then you re-add them on the device, it should correct the clients ability to interpret the email alert so it doesn't display as text. Give these steps a try, and the alerts should go away.