To increase your Google Page Rank, the best way is to build DoFollow backlinks. I recommend making useful and meaningful comments on DoFollow blogs.
Here's a good directory of DoFollow blogs: http://dofollow.info/ Please note that just spamming comments will not help at all.
Other ways to build backlinks is link exchanging with sites that are closely related to yours. Since you have a disposable email site, you could try to link exchange with sites talking about anti-spam methods. Don't do excessive link exchanging though, as Google does not like this.
Never sell or purchase text links/ads that do not hold the nofollow attribute. This is like buying PageRank, which can have an adverse negative affect your Google rankings.
The best PageRank comes naturally from having good content, rather than paid for (which includes link exchange).
And use the Canonical tag on your home page head section, since it redirects to a random query string email. This tag helps Google know that all of these URLs are the same.