Every Mail have to go though that MTA(Mail Transfer Agent) to get to the destination. This MTA do give us lot of services, like,
- Receives e-mail from client or another MTA
- Forwards to destination MTA
- May store for a while if destination. MTA is unavailable
- May scan mail for viruses and spam
May handle mailing lists and other features
All mail clients are configured with a local MTA. Simply all clients have a MTA. Client do not know how that mail is sent to the recipient. Client use SMTP(Simple Mail Transfer Protocol)(If you don’t know what is SMTP, it is OK just think it as set of rules which apply on that mail transfer. ) to send mail to the gateway.
Mail gateway looks up the right-hand side of the e-mail address in the DNS
An MX (Mail eXchange) record will redirect email sent to any user’s machine (email@example.com, for example) to a designated mail host. It tells the MDA where to route email.
The MX record uses preference values to specify the routing order–low value = high priority. In the example below, when mail is sent to norbert.dept1.cornell.edu the MDA (see Mail Delivery Agent above) tries to reroute the mail to mailhost.dept1.cornell.edu which has the lowest value, and therefore the highest priority. If that fails, it tries mailhost2.dept1.cornell.edu and finally mailhost3.dept1.cornell.edu.
norbert.dept1.cornell.edu 86400 A 126.96.36.199
norbert.dept1.cornell.edu 86400 MX 10 mailhost.dept1.cornell.edu
norbert.dept1.cornell.edu 86400 MX 20 mailhost2.dept1.cornell.edu
norbert.dept1.cornell.edu 86400 MX 30 mailhost3.dept1.cornell.edu
Using this IP mail is sent to the destination PC. To make the services reliable there are backup MX servers
Mailing list address specifies a special mailbox, called a list manager. List Manager sends copies of message to each address on the list sender does not need to know the list of recipients (like we have Google mail groups)