Question : step by step sendmail SMTP AUTHENTICATION in linux 7.3 and linux 9

step by step information for configuration sendmail SMTP AUTHENTICATION in linux 7.3 and linux 9

Answer : step by step sendmail SMTP AUTHENTICATION in linux 7.3 and linux 9

That's not what SMTP AUTH is designed to do. There's not a mechanism built in to Sendmail (or any other MTA) that will prevent it from accepting mail from a client that doesn't authenticate, and you wouldn't want that. If Sendmail operated in that manner you would not be able to receive mail from Internet sites that did not have a username and password that your server was prepared to accept. Since those who manage Internet mail servers are generally unwilling to do this it would effectively isolate your server from the Internet.

It is possible to use SMTP AUTH to limit what mail clients can do. If you set Sendmail up to refuse relay privs to everyone mail can still be delivered to your server from outside, but only clients that authenticate will be allowed to relay mail through the server. Most of the time one configures a mail server to allow relay privs to clients in the local domain or network, either as a result of a DNS reverse lookup or by including the network or IP's on the local clients in the access map. Removing that means that only mail sent from a direct login on the mail server or an authenticated client will be relayed.