Possible black list for hacking

Hi all, I find myself in a very bizarre situation.

I write a web application that basically records audits and other information. Now when an audit has been put onto my system it will send an email to three people.

It uses the domain name mail server to forward from the dedicated server where the application is running.

Now I have tested this, and it works. It works on the live site and my development site, but the recipients at the company xyz.com are not receiving emails.

So I ask their IT guy if they have anything that may be blocking it, and received no answer. So I tested the connection myself using the command line interface.

At first I did something wrong. I did not look up their correct preferred mx record and just telnet-ed onto xyz.com 25 (This was my mistake and ended up giving me a red hearing to chase). Anyway, it connected and I went through a test case and tried to send an email. The system I had connected to was an exchange system. The email did not get sent, and I was greeted with a CANNOT RELAY FOR so and so . So (still thinking I was on the right server) I emailed the IT guy and asked him about this, which he replied that it was my server saying I could not relay. This is where it gets messy..  I replied back saying I disagreed and that unless your system did an mx reverse lookup I cannot see how my server was referenced at all. So I then realised my mistake and found that they had in fact got 4 front end security servers (like sophos appliances). So I telnet-ed onto the preferred one and sent an email to the IT guy from it and then emailed him asking if he had received it. I don’t know why they have their exchange server forwarded to the outside world if they have the security email servers but that is not my worry I’m sure there is a reason.

So then I receive a very sharp email from the IT guy saying that I should not be connecting to their email system as I will get black listed and that I should be using my smtp server and such such and then a final warning, warning me never to connect to their smtp server again.
Now, my goal was to see why I could not send emails to their domain, or rather why it was that the clients were not receiving them. This operation of checking is actually outlined by a Microsoft KB for the recommended way of checking for email flow.

Now they are saying I have been hacking their system and that they will get me black listed world wide for such actions.

Did I do something wrong here? Aren’t email smtp servers open for such allowing connections. It’s not like I wanted or tried to relay messages off their server at all.

Many thanks for reading, any advice or statements that I’m in the wrong here even if it’s a moral thing would be appreciated.