One nice weapon to have in hand against spammers is an infinite number of email addresses. This happens to be something I have - actually, I have 2.5 infinite sets of email addresses (actually, not infinite, but something like 35^64 * 3 - I'm too lazy to calculate that number). This is because I have three domains of my own + one I share with a few family members, and any random address at those domains ends up in my inbox.
For people who don't have their domains, one common way to achieve this that's been used by many MTAs is to allow "plus" addresses - that is, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org are all treated as being the same address. This is useful, because if I get spam to, say, the email@example.com address, I know that Amazon has either sold my email address, or just been sloppy and revealed it to someone. I can then immediately consign any further mail sent to that address to the spam bin.
Yes, I've done this. firstname.lastname@example.org doesn't work any more (try sending mail to it!) because ICQ's directory published my address and led to too much spam. A certain person who may or may not read this, who is, either way, named after a snail, but apt to fly - well, their custom-built CMS didn't mask my email either, and I got spam on the address I'd used to sign up to their site. I did, of course, give them a gentle earbashing..
As well as "plus" addresses, some MTAs instead support the opposite syntax - "email@example.com" rather than "firstname.lastname@example.org". Both types of address are completely legal according to RFC2821.
Tonight, I decided it was time to ditch the hotmail address I've used as an MSN messenger address for a few years and move to something I actually read - people keep sending me emails there, but of course I don't bother reading hotmail - who wants to log in to a horribly clunky site just to read more spam?
I wanted to use an address that would end up at my gmail account, yet not my main gmail address - because, as mentioned, it's almost 100% certain that this address will start attracting bucketloads of spam the instant I make it public via passport.net (which you have to do in order to use MSN Messenger)
However... Microsoft refuse to believe that the "+" character is valid in email addresses - you can't sign up for a passport account with a + sign in the email address (even though it's perfectly valid!), nor can you send emails to such addresses from hotmail.
Gmail, on the other hand, only recognise the "+" syntax - so "email@example.com" is a valid working address, while "firstname.lastname@example.org" goes into a black hole.
So.. I can't do it. bah. humbug.