Sign-up email activation: How to deal with them not getting the email?

I have a simple web app and when you sign-up,开发者_JAVA技巧 you're emailed an activation link, which you need to click in order to enable your account and login.

What I've found is that some people are not getting that email, probably often because of spam but it's causing them to not bother or they try signing-up again.

What can be done to better handle this ?

Specify in the message to check your spam too. Also provide a option to get activation mail again just by entering the email address..

You could add an explicit message when they sign up informing them to check their spam boxes, beyond this it'd be hard to say what you can do to get past Every spam filter.