When new users register on our site, they're required to validate their email addresses by clicking a unique link in an email which they receive upon registration. For a small number of users, this doesn't work. We've checked our server logs and discovered that the validation links that these users are receiving appear to be modified in some way. For at least one user, spaces were inappropriately inserted into the URL, either by the user's email client or some other security apparatus in the client's environment. Has anyone experienced this before? Are there any known workarounds?