As part of a web application I am building, I must check if a particular email address exists. This check may be performed at around 1000 times an hour at a given server. Is there any mail server security policy that would prevent this?
Edit: I do not mean any particular server. Would there be any reason for throttling to be enabled anywhere.
Not only can you expect it to be throttled, but most likely that functionality will be turned off. This is because spammers use this to confirm email addresses.
If I were you I wouldn't use this technique as it sounds suspicious to me. You may find your site blacklisted as a spammer which definitely is counterproductive to your goals. Simply send a confirmation email to your users with a confirmation link inside. Until their email is confirmed limit their account or prevent access altogether. This functionality is commonly used and easy to implement.
The only way to be sure that an email address exists is to send an email to it and check that they opened it. The user might have very strict spam filtering that filters your email away. The email address still exists and yet you can't send anything to it.
