how to filter spam subscriptions?

Hello,

I just installed "BuddyPress Pending Activations plugin" because some of my subscribers didn't receive the activation emails. Now I can see most of the pending activations are spam but some of them are real users.

How should I deal with this problem?

Should I activate all users and apply some protection at login like captcha?

Don't Akismet take care of these spam users?

Please give me advice.

Thank you,
Luciano