Subscriber undeliverability reasons
The reason Buttondown has marked the subscriber as undeliverable. Undeliverable subscribers are not sent emails, and may be periodically removed from the system (or restored, if the reason is no longer valid.)
Access denied
Access to the subscriber's email was denied.
Disabled
The subscriber's email account is disabled.
Does not exist
The subscriber's email does not exist.
Domain blocked
The subscriber's domain is blocked.
Email blocked
The subscriber's email address is blocked.
IP blocked
The subscriber's IP address is blocked.
IP undeliverable
The subscriber's IP address is undeliverable.
Malformed
The subscriber's email is malformed.
On ESP denylist
The subscriber's email is on an ESP denylist.
Other
The subscriber is deemed undeliverable for an unknown reason.
Out of storage
The subscriber's mailbox is out of storage.
Problematic URL
The email contained a problematic URL.
Rate limited
The email provider, i.e. Gmail, acknowledges the message, but is temporarily refusing to send the message due to overall volume coming from the sender. Sender can mean a number of different things. For instance, it can mean that your specific newsletter is sending a high amount of volume. It can mean your domain is sending a high amount of volume. Or, in rare cases, it can mean that Buttondown itself as an overall system is sending too much volume. You do not need to change or retry any errors you see due to rate limiting. Buttondown will automatically handle that. However, if you see this error come up often, consider more regularly sending your email at a specific cadence, i.e. weekly.
Spam
The email was marked as spam.
SPF failed
SPF validation failed for the email.
Unreachable
The subscriber's email is unreachable.