Question: Does anyone check the domain of an email address as part of their verification steps? eg. Confirm that gmail.com exists if the user specified blah@gmail.com as their address.

---

I should note that in my webapp an existing user can forward invites to their friends. I have no need to verify those invites at all. Rather, I just want to warn my user if a typo etc. may be sending an invite to the wrong person. Is this even worthwhile to do?

Answer: 
You could do a dns lookup on the [mx record](http://en.wikipedia.org/wiki/MX_record). Here's an example at Code Project:  

<http://www.codeproject.com/KB/IP/dnslookupdotnet.aspx>

### [addendum]:

That should answer your question as asked, but as a side note I agree with @Franci that the old standby of sending a verification message is better. If someone's done everything else right to fool your validation, you're really not buying much in also checking the domain.
I usually let whatever mail component I use take care of domain validation. If it gives an error you can handle it in code, and decide if you want to show it to the user or not.