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 an email. If this occurs, we will attempt to send emails for up to 72 hours until the email is delivered. Normally, it takes between a few minutes to a few hours until the email is delivered.
The most common reason for an email deferral is sending too many emails 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 emails aren't spam.
Other possible reasons include the:
- recipient’s mailbox is full;
- receiving server doesn’t recognize your IP, and fears you might be sending spam; or
- receiving server doesn’t have any open ports to receive email.