I managed to export the email addresses of all commenters on a WordPress blog so that I could check if they’re using Twitter. This is fairly straightforward to do:
1. Using phpMyAdmin, export to CSV.
2. Using Excel, clean up the list:
2a. Import and set semicolon as the delimeter.
2b. Take the email addresses column.
2c. Filter to Unique entries only.
2d. Sort and remove the rows which are invalid email addresses (or not email addresses at all).
3. Use Notepad2 to change it into Gmail’s contact .csv format.
4. Import it on a Gmail account, and then use that Gmail account’s login on Twitter to see who’s in.
In my case, 23 people were already on Twitter 
I didn’t invite any who weren’t already on.
can you send me an email on the phpMyAdmin part of this export. This is exactly what I’ve been looking to do.
U just save my life my man !! I’ve tried it, successful ! Now, i have more that 2, 000 emails extracted from my website.
Fantastic! This helps SO much!