b2250e9c_lla_X_Mozilla_Status_explained_X_Mozilla_Status_Description
[Name] MSG_FLAG_SENDER_AUTHED [Value] 0x0200 [Description] 
If set, then this message's sender has been authenticated when sending this msg. This means the POP3 server gave a positive answer to the XSENDER command. Since this command is no standard and only known by few servers, this flag is unmeaning in most cases.
Christian Eyrich - Mozilla X-Mozilla-Status explained
Description