I had similar problem when i started playing more then a year ago.
The problem is not a the side of planeshift, but from the side of you're Internet Service Provider.
Some ISP's have an own spamm-spilter, besides the spamm-filter they offer to they're members.
The Validationmail from Planeshift is blocked by this first Spammfilter.
You can do nothing about it unfortunately.
My solution was to use a Hotmailaccount, because Hotmail does not block the Validationmail.