Hosting multiple websites on a single IP address

Hi, for the past 2 years we've been hosting our Exchange 2010 OWA on our public IP address. This has been working well in that we can type in webmail.domain.com and the users will be re-directed to the OWA logon page.

Last week, we went to implement 2x sub-domains which are required for some additional software that we have installed to improve the functionality of our database.

e.g. subdomain1.company.com and subdomain2.company.com

How would I go about routing traffic to the right destination? Below is a summary of the configuration so far:

Server 1 - Windows 2008 R2 - hosting webmail.company.com (Exchange 2010 Server)
Server 2 - Windows 2012 R2 - hosting subdomain1.company.com & subdomain2.intapeople.com (SQL 2014 Server)

Both servers need to use the same external IP address but I'm unsure on how to direct traffic to the correct sub-domain (whether it be webmail, subdomain1 or subdomain2).

Please could someone advise the best course of action in order to achieve this? My next step was to maybe purchase additional external IP addresses and host each sub domain on its own IP address but if I am able to host all 3 websites under 1 domain on the 2x IIS servers that would be great.

Would I need to put a re-direct / configure IIS on 'server 1' to route to 'server 2' or would it be done via another method.

Thanks in advance!