sendmail: 
 ,
  


   ...

    I:  sendmail  

    II:  sendmail  

    sendmail

   sendmail

  SpamAssassin

   Web-

   

    IMAP  

   KMail

   

         -
.      MUA (Mail User Agent    -
),          .
  MUA  mutt, Kmail, Mozilla Mail  Outlook. 
   MUA     (Mail Transfer Agent 
   ,   sendmail),    -
 .     MDA (Mail Delivery Agent   
 ,  procmail)      
.  Linux-  MUA      -
 ,      MUA  , , ()
SMTP-  Internet- (Internet Service Provider  ISP),   -
 POP (Post Office Protocol   )  IMAP (Internet Message Access
Protocol     Internet-).