One of my domains are dedicated just for my email. When I give someone an email address, it is unique for them, and them only. I also provide a public email address that does not accept HTML Mail, nor attachments. If you wrote me to the public email address, and you are legitimate email, you would get a reply from a dedicated email address that is for you.
The reason why I would do this is to attack would be SPAMmers, and scam artists. If a company gives my email address to a "marketing" campaign, I would receive the SPAM going to a particular address. I would than severe ties with that company by immediately closing the account with them, and killing the email address. This therefore allows me to continue relations with other companies without receiving the trash from the bad company. Since every company gets their own email address, I know who is at fault by simply looking at the address it went to.
The same would apply to those people I write to. It would seem as if individuals are smarter than most companies, and I haven't received SPAM to addresses I gave to ordinary people, however the problem with some of these are scams. Again, the address is killed, and it does not interfere with anyone else I write to.
It does require some management, and work. I use Mozilla(T) Thunderbird which has a great alias management feature. I simply add the alias account without setting up a special account. I can than select from a drop down menu of which address I want in the From section.
To this date, and with the exception of the public address, I would receive SPAM only once. Afterwards, I know who is at fault, and severe relations with them. I have the address killed later that day, and would not get SPAM again. This is done with a dedicated domain, and hosting with Dream host.