[help]still question about voicemail(resolved)

I have configured the ssmtp.conf,voicemail.conf and successfully send mail to some mailbox, but it seems that mails can not send to specific mailbox(such mailbox@yahoo.com). I have checked the help-files of such kind of mailbox, and it says they do not support visiting smtp and popl . If I m right , that is the point why all mails to this mailbox are lost.
But when I use mail command or ssmtp command in linux console, it works perfect.
And another thing, although I have changed the “servermail”, the "From"line still shows “hostname@asterisk”, why?
so I want to know which default client program of email asterisk is using and how can I use mailcmd to override it

pls help