Verizon has updated their receiving SMTP infrastructure and now has a limit on the number of messages you can send to their public SMTP gateway (firstname.lastname@example.org) per day.
If you receive a 554 response from a connection attempt to smtpin01.vzw.a.cloudfildter.net or smtpin02.vzw.a.cloudfilter.net, your site sends more traffic than their new public gateway allows.
That leaves you with a few options.
1) Register on their Enterprise gateway.
The URL you'll need to get started on the registration process it:
This PDF contains some basic information about what website to go to and how to start the process of registration:
You will need to contact your organization, city, county, state or regional Verizon Representative and request that they help you register as there are questions during the registration process that only a Verizon representative will be able answer.
2) Use a cellular modem.
A cellular modem is a device that provides a cellular connection to a system. PageGate can use this device to send (and receive) SMS messages just like a cell phone does, so you can bypass the need to rely on any carrier's internet gateways.
Multitech's MTCBA and rCell 100 series are examples of these types of devices.
3) Do both.
You can use the cellular modem as a primary method of delivering messages and have PageGate use a silent failover to the EMAG in the event the hardware has a problem.
Additional Details on the Verizon SMTP Public Gateway Issues