Recently I decided to install the WP Mail SMTP plugin into a WordPress blog to get around the shared server being blacklisted. The idea is to get WordPress to send emails through an external mail server after authenticating. However on one server, the test mail was failing: I was getting a timeout error.
After a little googling, I learned that some web hosts block certain outbound ports. But how to confirm whether my host was blocking port 587, used for SMTP over TLS?
Testing with portquiz.net
Enter portquiz.net. This brilliantly simple service is listening on all TCP ports and will respond to requests from http, telnet, nc, curl, and wget. Visit portquiz.net for examples.
I opened a Putty SSH session at each host and tested outbound port 587.
At one host, it fails:
Image may be NSFW.
Clik here to view.
That explains why I couldn’t send email from that host using WP Mail SMTP.
Fortunately, at the host that is blacklisted, port 587 is open and WP Mail SMTP works:
Image may be NSFW.
Clik here to view.
