I use a new e-mail address (alias) for every service I sign up to -- especially if it's a one-off transaction or a "short-term" relationship.

That way, if/when I start getting spam to that address or the address otherwise "leaks", I simply disable that alias and carry on.

(I've run my own mail servers for a loooong time so this is quite easy. It may be a little more difficult or involved if you use something like Gmail or whatever.)