It's possible for registered users to send email to other users through Wikitravel. For users who are logged in, each user page has an E-mail this user link on it. This should bring up the User email page.
The user email page has the following fields:
Note that email sent through Wikitravel is not anonymous. The recipient of the message will see the email address you used to register your user account in the "From" header of the email message. Also, users have the option to disable email delivery to their registered email address. So, there's no guarantee of delivery.
A better option for interpersonal communications on Wikitravel is editing the user's user talk page. This keeps the discussion out in the open, where other Wikitravellers can see it and possibly also respond.
Abusive or excessive email through the User email page is considered a grave misuse of Wikitravel, and is grounds for banning.