I have come across this PHP code to check email address using SMTP without sending an email.
Has anyone tried anything similar or does it work for you? Can you tell
Although this question is a bit old, this service tip might help users searching for a similar solution checking email addresses beyond syntax validation prior to sending.
I have been using this open sourced service for a more in depth validating of emails (checking for mx records on the e-mail address domain etc.) for a few projects with good results. It also checks for common typos witch is quite useful. Demo here.