Iis – Multiple domains (with & without www prefix) on same server, running the same code

In this case you would need separate ports if they were on the same IP, or separate IPs if you wanted them on the same standard SSL port (443). IIS doesn't support reading host headers and redirecting using SSL. You can use the same wildcard certificate without any issue, but you would need something inbetween IIS and the client (like Microsoft Forefront Threat Management Gateway) in order to do routing by hostname over SSL. (I hope that makes sense)

The reason this happens is because the connection is encrypted and the certificate is validated before the HTTP header is actually sent, so at that time IIS has to know what site it's using beforehand. Now, Firefox does send the hostname in with the initial encryption request but I'm not sure if IIS supports that (or if any other browsers do).

The First Few Milliseconds of a HTTPS Connection has an incredibly in depth description on how HTTPS generally works (through a special debug build of Firefox). As you can see a few paragraphs in TLS supports a server name extension, but as far as I know IIS does not support that extension.

1. For email, I don't think you can do this with DNS. The only time DNS is involved with mail is for determining which server to send mail to for the requested domain. So whilst you can have the MX records for both domain1.com and domain1.net pointing to mail.domain1.com, say, you will need to configure that server to accept mail for both domains, and route it to the correct mailbox as appropriate. Exchange will do all of the above out of the box.

For web requests, (and this answers #3 too), it depends on whether you care about the host name that ends up in the address bar of the browser. If you don't then you could just CNAME www.domain1.com to www.domain1.net, and as long as you have both hostnames as vaild host headers for the site in IIS/Apache, the page will load and all will work. I wouldn't recommend this however as all it takes is one absolute href and the user is bounced to the other domain, not to mention issues with SSL and wider business branding problems, SEO, the list goes on.

To do that properly, use a redirect rule and bounce all traffic to one domain.

2. IIS redirect is the neatest way, keeps everything consistent. You could just add A records for both in DNS and add both as accepted host headers for the site in IIS though. Up to you.

3. As 1. but bear in mind that if you want to use SSL you will need a dedicated server IP for each site, so it might be simpler to redirect everything to one place and then secure that.

HTH