Our SMTP server works off of 2 authentication methods. The first is the standard SMTP authentication. This means that the sending SMTP server will pass along the username / password during the relay and we know who you are, how much you can relay, etc.
The second method of authentication is POP before SMTP. This works for many people who cannot get their mail server to provide smtp authentication. POP before SMTP works like this: Your server checks a POP3 mailbox on our server - this mailbox is the relay account you've setup on our site. Once you've authenticated using POP3 you are now allowed to send, from that same IP address, within the next 60 minutes. So, if you have a little utility that checks the pop3 mailbox once per hour you can relay outbound.
I've helped many people with Exchange 5.5 get this working. Since Exchange 5.5 does not include any SMTP authentication methods then we have them run the little client utility. There is a nice one here:
Notify.zip
This utility runs on windows and simply checks a pop3 mailbox at a specified interval. This will keep your IP address open for relay using our server. Please do not set the interval for this utility for anything more than every 20 minutes or so since the time to live for the authentication is 1 hour anyhow.
I am familiar with quite a few mail servers out there and there is always a way to make them work - sometimes you just have to perform some stunts to trick em
Also - we have the ability to enter an allowed IP range - although this defeats the purpose of what we are trying to provide. Allowed IP ranges do not get placed under the quota limits - and they also can be potential spam avenues. We work hard to not let our IP blocks get listed in these RBL and other lists so that you can continue to enjoy the quality smtp services we offer. Many other ISPs and providers like us get listed in RBLs and such and then it affects all other clients using that service.
Thanks!
Sam