Iis Smtp Help

This topic is covered so many times, but in all the searches I've done I just can't get my head around how to make this work.

I have a server running 2003 Server (IIS 6).
I have the SMTP sever configured like so.

General Tab
-Server response to all ips requests on port 25.

Access Tab
-Authentication
--- Anonymous Checked
--- Basic Checked, TLS Encryption Checked, Default Domain = webserver (pc name)

-Connection
--- All

-Relay
--- Block all except listed addresses
-----(Listed the actual internet IP address as well as the internal network ip. Also listed domain main the server responds to)

Delivery Tab
-Outbound Security
---Anonymous

-Advanced
---FQDN = "webserver" (pc name)
---Smarthost = " "
--- Reverse DNS = checked

-----------------------------
The problem.
The mail server works sometimes and sometimes it doesnt.
I have and CMS installed that uses php to route mail through the server. It access the server by it's ip address and sends username and pass. The SMTP receives the mail properly but if the mail is being sent to and outside domain it'll get stuck in the Queue Folder. If the mail is being sent internally for exmaple the website would be haha.com and I'm sending the mail to me@haha.com it' sends fine.

If I send mail through outlook, it sends the mail fine to external domains, but the mail is always tagged as bulk.

I have MX records for my domains setup to point too mail.whateverdomain.com on all registered domains. I was under the understand that by performing the reversedns lookup, it would qualify my mail and not tag it as bulk.

Do I need to change my FQDN to something else or is "webserver" fine. It matches the tcp/ip network name and clicking the button to validate it returns a valid response.

So why is mail getting stuck and if it is sent, being tagged as bulk?
Any help would be GREATLY appreciated.

There are all sorts of anti-spam filters that can interfere with your mail. As you mentioned, one common reason is if your smtp server doesn't have a reverse DNS entry. Does your smtp have a reverse DNS entry in your domain zone?