For beginner forum admins, or what is the simplest method of checking an individual subscriber
The good thing in collecting the e-mail address of the subscriber is, that you can check if that e-mail address is used by someone or it’s just an random string.
How? Just google it, and there is near 80% chance to get some information about, or connected with the specific e-mail address, such as another blog post, or a public user listing, or a spambot catch page. If you can’t get any information about the subscriber, do’nt worry, there is another method to filter it(him/her) out. This latter method takes some time, as you have to check, if the subscriber is active or not, posting useful informations or valid questions on the forum. If the subscriber is not active (logged in a long time ago or never), posting nonsense, you can easily delete the related user account. This is why you have to keep your forum moderated.
If your forum is too large for one moderator already, choose the most active and most loyal users, and ask them if they are willing to moderate certain sections or the entire forum for you. Supervising 4 or 5 people instead of 400 is much easier, and they will do the rest of the job.
Returning to the googling method:
The method is not foolproof, but lets you filter out the most obvious and most known spam attempts, and that’s quiet enough. Be aware. As your site grows in content ands popularity, the chance to get spammed grows exponentially. Many good forum software has built-in capability to help in filtering out these scams, but human presence is always needed.