I am getting desperate and start to question my own sanity so maybe one of your can give an explanation for some seemingly strange Exchange 2013 behaviour.
I'm trying to change the url of a smarthost which is used by our internal Exchange 2013 to deliver mails to any external domain. This setup has worked for a few years but due to problems with the smarthost host, I decided to setup my own smarthost externally. That's not the problem.
In order to use the new smarthost I first simply edited the smtp send connector which was already configured to use a smarthost and changed its smarthost url. It had no effect. When I look at the send connectors smtp send logs I can see that exchange is still connecting to the old smarthost. Exchange is however using the new basic auth credentials which wont work with the old smarthost.
I also tried to create a new send connector and configure that one to use the new smarthost, I was supprised to see that Exchange still tried to connect to the old smarthost, which was not present in any config anymore (to the best of my knowledge). It even printed the new sen connectors name in the logs, so it was using the right connector.
I tried restarting the transport service and I also rebooted the server.
Displaying the send connector's properties in powershell shows correct values.
Why is it still connecting to the old smarthost and how do I change that?
Update: Niko.Cheng's comment was right. After using the new smarthost's IP as URL everthing worked as expected. But I still don't know why it did not work using a regular url. DNS lookups are working, and even if they weren't Exchange should not simply fall back to an old and outdated url value.
