| Interface | IWeaklyAuthenticatedPrincipal | The principal has been weakly authenticated. |
| Interface | ISignedMessage | A message that's possibly signed with an OpenPGP key. |
| Interface | IMailHandler | Handles incoming mail sent to a specific email domain. |
| Class | EmailProcessingError | Something went wrong while processing an email command. |
| Class | UnknownRecipientError | Error raised when an email or person isn't part of the recipient set. |
| Interface | INotificationRecipientSet | Represents a set of notification recipients and rationales. |
| Class | BugTargetNotFound | A bug target couldn't be found. |
| Interface | IEmailCommand | An email command. |
| Interface | IBugEmailCommand | An email command specific to getting or creating a bug. |
| Interface | IBugTaskEmailCommand | An email command specific to getting or creating a bug task. |
| Interface | IBugEditEmailCommand | An email command specific to editing a bug. |
| Interface | IBugTaskEditEmailCommand | An email command specific to editing a bug task. |