Sendmail service
DNS,domain name server,usually has a cache server in the font which has a special database.If the request are listed in the database of cache server,turn the specified IP address to user.If the request could not be found,the cache server pass the request to the really DNS server to resolve the address.The /etc/named.conf file contains the parameters of DNS setting,and the /etc/named/named.ca is owned by cache server.The file named “named.ca” will ofen be updated,there are total 13 root DNS server all around world,these root machine’s IP address are indicated in the “named.ca” file.
E-mail system has two main partitions:UA(user agent) and MTA(Message Transfer Agent).US are installed in the client used to write and read mails,many softwares are developed for US,for example,Outlook express,Foxmail or Evolution of Linux.MTA is also called mail server which provides storage and re-sending the mails utilities.There are three common protocol:SMTP,POP3 and IMAP.SMTP(simple mail transport protocol) put the mail to the target address step by step.IMAP(Internet Message Access Protocol) acts like POP3 which is more popurlar.
Linux Mail Server are the following:Sendmail,Qmail,CommuniGate ProMessaging Server for linux,Mail studio 2000.
Sendmail service is installed in the Linux by default.It re-writes the mail’s address,if the address is local,the mail will be saved at /var/spool/mail.
# /etc/rc.d/init.d/sendmail start # /etc/rc.d/init.d/sendmail stop # /etc/rc.d/init.d/sendmail restart