Disable activation via email requirements

Hi! My users are experiencing some problems with signing up to my site - they don't receive the activation email when they sign up. I thought this was rather strange as I had received the email perfectly. So I did a test. I told 3 people to sign up to my website (different houses, different providers). 2 people signed up successfully. The other failed.

I'm on BT Home Hub.

My friend who signed up successfully is also using BT, but a different kind of wireless station.

My friend who didn't get the email is on TalkTalk.

I'm not sure what service my other friend who signed up successfully is using.

 

So, I was wondering if there was a way so nobody would have to click on the link in the activation email, just be able to log in straight after registering?

 

Thanks so much!