I'm getting the same error. I'm using SmarterMail MSI - Build 6996 

Windows 2016 / IIS10.0 - I have been installing lots of SmarterMail Server and this is my first time; got stock in this step. I tried different entry but nothing works.

Please help fixed the issue. * Darren DG

Ditto, we got this on a new server setup (but for SmarterStats) for a client.

Hello everyone. I just tested the MSI/EXE installers of our latest minor releases and was not able to reproduce these issues. I recommend opening IIS and verifying there is not an existing site with the same settings. After that check the Windows Services Console for any references to the SmarterMail Web Server from previous versions as this might be blocking port access during the installer process. Lastly, please try a restart on the server and give this another go to see if it has freed up what ever resources were needed. If you continue to have issues with this I recommend you submit a support ticket. 

This was a brand new server, nothing was on it other than IIS and SmarterStats. I just ignored it and created the site manually.

Thanks echoDreamz. I just tested with the SmarterStats MSI installer as well and was not able to reproduce this issue. With SmarterStats we offer two installers:

1. EXE based installer

2. MSI based service-only installer

The MSI installer does not actually include the IIS configuration functionality as its only to facilitate service deployment, and is not used on the primary (web server) SmarterStats deployment. There might be some confusion going on between the EXE/MSI, so I recommend re-downloading the installer to be safe if you run into these issues again in the future. 

I always download the exe, never even used the MSI installer. But this was on 2 completely (brand new) different servers. 1 Server 2019 and 1 Server 2016. Both had IIS installed with .net and all the other requirements, but would refuse to create the site through the installer.

As I said, no biggie, I told the installer to move on and I created the site myself.

Michael, I'm sorry to hear you're running into this error as well. This shouldn't be failing validation as best I can tell, so I recommend getting a support ticket submitted on this so we can take a look for you.

In the meantime, can you try configuring the hostname localhost to see if that helps it pass validation? Alternatively, you can manually create the SmarterMail application pool and IIS site as well. I hope this helps!

Thanks Kyle! I manually created the SmarterMail pool and site first and installed SmarterMail after, it OK now.

That is great news Michael, you're very welcome. We've attempted to reproduce these issues in-house using our own deployments and configuration backups of some customer environments, but each time we're unable to reproduce, unfortunately. If you end up finding out what's different in your environment please don't hesitate to reach out, as we'd love to get to the bottom of this. Have a good one!