550 Relaying Denied message when trying to send email fom Outlook from Sendmail server

You don't want to allow just anyone who wants to pretend to be you to send outgoing email through your server - that's what's known as an open relay.

Is this server local?  Or are you trying to send out domain based email for a remote server?  If it's the later, you most likely want to send out through the SMTP account provided by your local ISP;  you can still send out configured as you@yourdomain.com - it's just your isp's outgoing server that handles the outgoing delivery.

Hello:
Thank you for answering.
The Red Hat Linux es server is not local It is at a remote location. My ISP is Pac Bell my MX record shows the following:
smpt-relay.pbi.net
Can you tell me how I could use my ISP for relaying from my remote server.
Thank you
Keith Henriques

Set up your identity with your return email address (reply-to and from) as being your domain-based email address.  Then, for the outgoing email, use your Pac Bell SMTP server.

You haven't mentioned which version of Outlook you are using;  the procedures are similar, but vary slightly with each version.

A guide for Outlook 2000 can be found here, that is good for reference:

http://www.comptechdoc.org/applicat/outlook/guide/outaccount.html

Basically, using the screen shots on this page, you'd set up your 'Display Name' as a text string (Perhaps something like Keith Aris), and your Email Address to your domain-based email address.  

For the Email Server Names, your incoming POP3/IMAP server would be the server from which you physically retreive your email.  This might be your domain-based server, or if email is simply forwarded from your domain to your Pac Bell account, it will be your Pac Bell Account.  For your outgoing SMTP server, it will be your Pac Bell SMTP server.

The Account and Password refer to the account and password for your incoming email account - i.e. the username and password from the server where you physically retreive your email...

Hello Periwinkle:
The problem I have is that when I use :
smpt-relay.pbi.net   (This is the mail server I get using dig to search my MX records)
I get a message from outlook telling me I am unable to connect to my outgoing mail server.
Do you have any ideas on how to connect correctly to my pbi.net mail server?
Perhaps I need to Call SBC for an answer if it is not listed somewhere.
Thank you in advance
Keith Henrques

You could also set up some type of SMTP authorization or POP before SMTP.. These will check your server for credentials before allowing you to send e-mail out..

Here is a good how to on it:
http://www.simpaticus.com/linux/howto/html-single/Sendmail-SMTP-AUTH-HOWTO.html