Question

I’m using PHP’s SwiftMailer library to bulk send emails (following CANSPAM and RFCs).

Everything works fine until I run across a domain that does not have a corresponding MX entry in the DNS. At that point, my script just hangs — I’m assuming it’s because sendmail hasn’t returned. This can last just a few minutes, or it can last many hours.

I have confirmed that the addresses my script (slash sendmail) hang on are those without a DNS MX entry. Everything else sends fine.

Is there a way I can check if the DNS MX exists inside of PHP before I attempt to send the message? Is this scalable (i.e., will that extra lookup on the DNS really slow me down, or will it be fine b/c then the MX is cached locally for sendmail to use in delivering the message)?

Thanks for your help

— UPDATE —
I tried the solutions below, which helped me narrow down what the problem is. It seems it’s not a question of whether or not the MX entry exists. The problem is that the DNS lookup is taking forever to return. Is there a simple way I can set the timeout, so if DNS doesn’t return in < 5s, I can move on?

Answer 1

getmxrr(substr($email,strrpos($email,'@')+1),$hosts);
if (!$hosts)
    echo 'No MX record found';

You can also try this to prevent blocking (there are no options for adjusting getmxrr timeout):

if (!@fsockopen(substr($email,strrpos($email,'@')+1),25,$errno,$errstr,5))
    echo 'No MX record found';