IIS and Mail Server on same box?

I have a Windows 2012 web server. On it I have IIS and all my websites setup.

I installed a mail server on this same box. I set it up in the firewall to use allow TCP over these ports, etc. It is working fine.

But now all of my websites are stopped. I tried to start them again and get this error:
>>The process cannot access the file because it is being used by another process

I looked this up and found this:
https://support.microsoft.com/en-us/kb/890015

It says it could be caused by this:
•Another process is using port 80 or port 443 on the computer that is running IIS. By default, IIS uses port 80 as the default TCP port and port 443 for Secure Sockets Layer (SSL).

Can a mail server and web server live on the same box? If so, how can I set them up to live nicely together?

This is Icewarp mail server and I am hosting on Rackspace if that helps. I also added a reverse DNS to the admin panel in Rackspace for the IP address and attached it to my mail server name: mail.blah.com

thanks!