> A deferred message event, or deferral, is simply an event our system has received back from the receiving server, that tells us that the receiving server has temporarily limited access to their system. You can think of this like a busy signal.
> It does not mean that your message will not be delivered. Rather, it is a signal that your message will not be delivered immediately. This can happen for a variety of reasons. Some of the most common reasons a message might be deferred at an inbox provider are that the inbox provider is seeing too many spam complaints for your email that has already been delivered or that the receiving server is having technical issues at that time.
> When our system sees your mail being deferred at a particular inbox provider, we will continue to try to deliver that message for you for up to 72 hours. If a message to a recipient is deferred for more than 72 hours, that deferral will turn into a block. Otherwise, it will result in a delivery event once the message has been accepted by the receiving server.