Autopilot is designed with deferrals (also known as "throttling") in mind.
If an email is deferred, you will see the following message in a contact's activity feed:
This means that the recipient's mail server has temporarily refused delivery of a message. If this occurs, we will attempt to send messages for up to 72 hours until the message is delivered. Normally, it takes between a few minutes to a few hours until the message is delivered.
The most common reason for an email deferral is sending too many messages over a given timeframe to a particular email service provider. Email providers, such as Yahoo, can sometimes throttle incoming mail temporarily to prevent the server from being flooded and in order to check that the messages aren't spam.
Other possible reasons include:
- the recipient’s mailbox is full;
- the receiving server doesn’t recognize your IP, and fears you might be sending spam; or
- the receiving server doesn’t have any open ports to receive email.