Consider the problem faced by Eric Hammond, who wished to use different delimiters for tag strings in GMail addresses other than "+". Instead of hacking up a solution on infrastructure he owns, he took advantage of the capabilities of AWS and crafted a solution that is completely automated for him and also available for any of us to quickly use provided we are willing to use Google Apps for Business for email and Route53 for DNS.
The solution is an AWS Cloud Formation template that lets you fill in the blanks to specify the domain you own and a few other operational customizing parameters. The result is a ready-made infrastructure sitting on AWS that takes advantage of Route53 for programmatically creating an MX record and bootstrapping a scaling group of instances on EC2. These instances host a postfix server configured to act as an email relay that will transform email addresses containing "-" in the local part of the address to the GMail supported "+" characters and ultimately relay to GMail.
The automation and hosted nature of cloud-based providers allows such problems to be solved and shared in a very general way, as Eric has done. This particular example also demonstrates why you should be thinking about cloud-based solutions to solve problems even if you aren't interested in running your applications and data processing on cloud and IaaS providers.