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. 

Consumer versus Non-Consumer Text Messaging | T-Mobile Support

The e-mail to text gateway is a legacy system that may eventually be decommissioned in the future. It is designed for low volume consumer traffic only and cannot handle a significant volume of messages. For that reason, all non-consumer messaging is prohibited on the e-mail to text gateway, and even high volume consumer messaging may be blocked as it can impact the system's ability to handle messages for all customers. If you need to send non-consumer or high volume consumer messaging, please seek out an aggregator as their connections can handle these message volumes.

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) page.