Part of lp.services.messages.interfaces
| Interface | IMessageSet | Set of IMessage |
| Interface | IIndexedMessage | An IMessage decorated with its index and context. |
| Class | IndexedMessage | Adds the inside and index attributes to an IMessage. |
| Interface | IMessageChunk | Undocumented |
| Class | QuotaReachedError | The user-to-user contact email quota has been reached for today. |
| Interface | IUserToUserEmail | User to user direct email communications. |
| Interface | IDirectEmailAuthorization | Can a Launchpad user contact another Launchpad user? |
| Class | UnknownSender | Raised if we cannot lookup an email message's sender in the database |
| Class | MissingSubject | Raised if we get an email message with no Subject: header |
| Class | DuplicateMessageId | Raised if we attempt to store a new email with an existing Message-Id |
| Class | InvalidEmailMessage | Raised if the email message is too broken for us to deal with. |