Error codes returned as integers can be one of the following :
enum {
MAIL_NO_ERROR = 0,
MAIL_NO_ERROR_AUTHENTICATED,
MAIL_NO_ERROR_NON_AUTHENTICATED,
MAIL_ERROR_NOT_IMPLEMENTED,
MAIL_ERROR_UNKNOWN,
MAIL_ERROR_CONNECT,
MAIL_ERROR_BAD_STATE,
MAIL_ERROR_FILE,
MAIL_ERROR_STREAM,
MAIL_ERROR_LOGIN,
MAIL_ERROR_CREATE, /* 10 */
MAIL_ERROR_DELETE,
MAIL_ERROR_LOGOUT,
MAIL_ERROR_NOOP,
MAIL_ERROR_RENAME,
MAIL_ERROR_CHECK,
MAIL_ERROR_EXAMINE,
MAIL_ERROR_SELECT,
MAIL_ERROR_MEMORY,
MAIL_ERROR_STATUS,
MAIL_ERROR_SUBSCRIBE, /* 20 */
MAIL_ERROR_UNSUBSCRIBE,
MAIL_ERROR_LIST,
MAIL_ERROR_LSUB,
MAIL_ERROR_APPEND,
MAIL_ERROR_COPY,
MAIL_ERROR_FETCH,
MAIL_ERROR_STORE,
MAIL_ERROR_SEARCH,
MAIL_ERROR_DISKSPACE,
MAIL_ERROR_MSG_NOT_FOUND, /* 30 */
MAIL_ERROR_PARSE,
MAIL_ERROR_INVAL,
MAIL_ERROR_PART_NOT_FOUND,
MAIL_ERROR_REMOVE,
MAIL_ERROR_FOLDER_NOT_FOUND,
MAIL_ERROR_MOVE,
MAIL_ERROR_STARTTLS,
MAIL_ERROR_CACHE_MISS,
MAIL_ERROR_NO_TLS,
MAIL_ERROR_EXPUNGE,
/* misc errors */
MAIL_ERROR_MISC,
MAIL_ERROR_PROTOCOL,
MAIL_ERROR_CAPABILITY,
MAIL_ERROR_CLOSE,
MAIL_ERROR_FATAL,
MAIL_ERROR_READONLY,
MAIL_ERROR_NO_APOP,
MAIL_ERROR_COMMAND_NOT_SUPPORTED,
MAIL_ERROR_NO_PERMISSION,
MAIL_ERROR_PROGRAM_ERROR,
MAIL_ERROR_SUBJECT_NOT_FOUND,
MAIL_ERROR_CHAR_ENCODING_FAILED,
MAIL_ERROR_SEND,
MAIL_ERROR_COMMAND,
};