SMTP help

Not sure if this is the right forum to post this in but i am getting started in trying to learn the smtp server.
This is the error i'm getting.
smtp error 0xc00402c7
message sender was <>.
Only get this error when i send emails using a web program i'vewritten. It will send to my gmail account but not to my emailaddress that is on this same domain. I'm not sure what to do tofix this. I've searched for solutions but they either didn't helpor i didn't really understand what they were saying.
Any help would be appreciated.
Thanks in advance.
Some smtp servers require a valid domain name. Try setting the sender with a valid email address (i.e., your GMail one).

Ok the sender is the same for all emails sent. The domain namethat is being used is hosting on the same server as the smtp.
info@.website.com
myname@.company.com
would this make any difference?
send to myname@.gmail.com from info@.website.com works
send to myname@.company.com from info@.website.com (Both on same server) doesn't work.
i will try using a different email address and see if that work otherwise any ideas?

You can go to the MSDN and search for System.Web.Mail.smtpMail class. There is a lot of information.
Just to clarify some things:
You need to have a SMTP server accessible from the machine you run the IIS with anonymous access permitted.
This is due to the fact that the smtpMail class does not log-in onto the smtp server.
The smtpserver must use the TCP port 25 and your lan /wan must support this traffic.
If you are running some Firewall be aware to open the apropiate ports.
For test purposes MS Exchange Server is a little bit difficult to setup as an anonymous relay agent.
There are small (and free:) smtp servers easy to configure to accept anonimous senders.
Please, protect the server in a way that only authorized machines can reach the server. Otherway you can be SPAMmed even infected easely.
Hope this helps.

I am still have problems with this thing. I changed the emailthat is the from info@.site.com to my gmail and it still bounced. everything is filled out to, from, subject etc. I tried usingthis format email@.compay.com <email@.company.com> but that didn'twork. Any ideas would be greatly appreciated. It's not onlywith the emails from out domain. 900 of the emails I sent out hadsimiliar errors. But 1600 of them went through. I'm doingmore research not finding much tough.
any help would be appreciated.

Check the SMTP server logs for details of what happened. They should show the connection attempt, as well as the response form the other side. Some of the more common issues with SMTP deliveries and rejections, outside of coding errors are:
Unable to resolve destination MX address
Missing or incorrect destination
Missing or incorrect sender
Using a SMTP server on a dynamic IP address (Big indicator that the email is SPAM)
SMTP server is blacklisted (Even bigger SPAM indicator)
No reverse DNS (Also SPAM indication)
Reverse DNS points to wrong domain (Fortunately few system see this as SPAM, but still an issue)
Strange sending path or potentially spoofed sender (Such as a message from a US domain sent to a US domain by relaying through a Korean server)
Large number of messages sent too close together (indicator of mass mailing, potentially SPAM)
Jeff
I am suspecting a problem with your DNS server and that could be the reason why you are unable to deliver message to internal users;
May you could use the following URL to check the mail relay;
http://www.abuse.net/relay.html