ASP.Net, Explicit SSL - how to connect?

[MC9000]

Hi all,
I have a website in ASP.Net that needs to connect via SSL (ASP.Net does not support Implicit SSL, so I can only connect via Explicit SSL).
I've tried dozens of combinations of ports & settings on AMS to get this to work.
It SHOULD work on Port 587 (what the port number is set to) as this port is for Explicit SSL, however, I cannot telnet to this port unless the Implicit SSL checkbox is checked (which looks like a catch-22). I can telnet to 25, but if I try to use port 25 (as you're supposed to do for Explicit SSL), I get "The sender's domain requires authentication or is not a valid user."
From the same machine, I use Outlook with the same credentials and it works just fine. I bought an SSL cert for my domain, so it's not a self-signed certificate problem.

I can connect fine w/o SSL, so the account and password are fine, but I don't want to send passwords in the clear!

Regardless - if ANYONE has successfully connected to AMS from an ASP.Net or any DotNet application, please post your code!!!! I've spent an entire weekend with every possible combination of settings, but no joy. I was about to upgrade to the version 3.X of AMS (from the last 2.X version), but will have to find another mail server if I can't get this to work.

[Code Crafters]

The error "The sender's domain requires authentication or is not a valid user." is the problem here. This is caused by you failing the Sender Domain Check SPAM filter which requires you to meet one of the following requirements:

Client Must Have Relaying Access - SMTP authentication completed or otherwise authenticated
Sender Email Address Must Exist Locally - local user as SMTP sender

To get round this the best option is to add the IP or host of the ASP.Net machine to the SPAM white list so that this machine doesn't have to pass any SPAM filters to send email; as long as it's secure to do so of course.

[MC9000]

Thanks!
That was the problem: "Sender Email Address Must Exist Locally " - I had a dummy email address in the application called noreply@mydomain.com that was not an actual account. I set up the account and got it to work.