[CentOS] sendmail security

hi all i am using sendmail mail server, i have configured SASL+TLS+MailScanner+Spamassasin+.Procmail and its working fine, but there is one problem when i am doing telnet to my server on 25 port and using "mail from " command to send mail by any user like abc@gmail.com or any user @mydomain then sendmail is not able to verify sending user , so plz help me how can i verify the real sender means i want only my domain real user can sendmails .and when i am using mail clients then its working fine . prolem is occuring when , when i am doing telnet directly to smtp port to my server

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