I'm using mutt&postfix on CentOS 6.2: mutt-1.5.20-2.20091214hg736b6a.el6_1.1.x86_64 postfix-2.6.6-2.2.el6_1.x86_64 When I try to send mail to my company mailbox, I receive an error: mutt -s "test" [email protected] < /home/mail.txt error from postfix: : host out1.ourcompany.com[10.30.17.100] said: 555 Syntax error (in reply to MAIL FROM command) Then I try to use service sendmail as SMTP server, but also failed: **----- The following addresses had permanent fatal errors ----- (reason: 555 Syntax error) ----- Transcript of session follows ----- ... while talking to out1.ourcompany.com.: MAIL From: SIZE=667 <<< 555 Syntax error 554 5.0.0 Service unavailable** Any body can tell me why? Thanks!!!! I can make sure DNS is OK, and I set realname "root@myserver" in /etc/Muttrc