Rate-limited, can our application get white listed?

Unfortunately, email to text is not designed for commercial messaging and should only be used for consumer-to-consumer messages. We don't have the ability to whitelist anyone on this service because spammers tend to piggyback on the network configuration of the bulk messages that are sent through the it (by no fault of anyone but the spammers). The email to text service has some pretty aggressive spam filters and they won't be relaxed until spamming is eliminated. The page that Fireguy linked does have an FAQ toward the bottom that discusses the email to text limitations at little bit. 

Mensajería de texto para consumidores versus no consumidores | Asistencia de T-Mobile

El gateway de email a mensaje de texto es un sistema legado que posiblemente sea descontinuado en el futuro. Está diseñada únicamente para tráfico de consumidor de bajo volumen y no puede manejar una gran cantidad de mensajes. Por esa razón, todos los mensajes que no sean para consumidor están prohibidos en el gateway de email a mensaje de texto, e incluso podría bloquearse la mensajería de consumidor de alto volumen ya que podría afectar la capacidad del sistema de administrar los mensajes para todos los clientes. Si necesitas enviar mensajes que no son al consumidor o gran volumen de mensajes al consumidor, busca un agregador ya que ese tipo de conexiones pueden manejar ese tipo de volumen de mensajes.

When companies are sending messages to customers, certain federal (CTIA) and carrier (not just T-Mobile) guidelines must be followed to ensure everyone's protection and to avoid spamming of any kind. That is why using an aggregator is going to be a better option for you than trying to continue on the email to text options. Aggregators are vetted to ensure they are following the code of conduct so their services can be flagged differently through our messaging systems and you will not be blocked as a spammer. 

If you do want to get in touch with someone about the situation you can write to our Customer Relations team at the PO box listed on our Contact Us (t-mobile.com) .