If a user tries to send a message through our systems and receives the error: 

"550 This recipient recently bounced. Try again later" 

This means that a message to this recipient has been bounced by the recipients mail server in the past few hours. 

As a result we will not send new messages to recipient email addresses that have recently bounced. After a number of hours we purge the bounced recipients and future messages sent to the bounced recipient will be attempted as normal by our servers.