I have followed the guides on setting up postfix relay to my account at network solutions. I added these to main.cf: inet_interfaces = localhost relayhost = [mail.mydomain.com]:587 smtp_sasl_auth_enable = yes smtp_sasl_security_options = noanonymous smtp_sasl_password_maps = hash:/etc/postfix/sasl_password smtp_use_tls = yes smtp_tls_CAfile = /etc/pki/tls/certs/sendmail.pem The username and password are correct, and all these options work fine from thunderbird on a windows box in my local network. I get no errors on postfix restart, but when I try to send an email from the centos box, I get this: Apr 26 17:00:33 host postfix/smtp: C9C1D80075: to=<campbell at somedomain.com>, relay=mail.mydomain.com[xxx.xxx.xxx.xxx]:587, delay=0.87, delays=0.08/0.02/0.72/0.04, dsn=5.0.0, status=bounced (host mail.mydomain.com[xxx.xxx.xxx.xxx] said: 503 you must authenticate first (#5.5.1) (in reply to MAIL FROM command)) Why is tls not authenticating? Under centos 5 I used sendmail, and it all worked just fine. -chuck -- ACCEL Services, Inc.| Specialists in Gravity, Magnetics | (713)993-0671 ph. | and Integrated Interpretation | (713)993-0608 fax 448 W. 19th St. #325| Since 1992 | (713)306-5794 cell Houston, TX, 77008 | Chuck Campbell | campbell at accelinc.com | President & Senior Geoscientist | "Integration means more than having all the maps at the same scale!"