I was working at a client site the other day. I received an unusual request to fix a technical problem. A customer was having a problem sending an email while using Microsoft Outlook, a pop3 email client. The customer can retrieve email, but could not send messages out.
When you hear of such a problem, it usually points to a misconfiguration of the SMTP server in the pop3 client software. But this was not the case. Upon further investigation, I learned the internet service provider, SBC Global Communications was blocking the SMTP port 25.
This is fairly common practice by a few internet service providers (ISP) while trying to cut down on unsolicited emails (SPAM). In addition, ISPs usually require customers to authenticate on their own SMTP servers.
The authentication poses a problem if you are trying to provide a free Wi-fi service to your customers. The last thing you need to do is to share your SMTP username and password with your customers.
What to do? There are two ways to fix this problem.
1. Have the customer change their SMTP server from port 25 to port 587.
2. You need to contact the SBC’s website and fill out an online form to “opt-out Port 25.”
Option number one is a temporary fix. Changing the SMTP from port 25 to port 587 involves changing the SMTP configuration on the pop3 email client, in this case Microsoft Outlook. You will need to do this to every customer that is using a pop3 email client. SBC documents this fix on Yahoo’s website.
Option number two is the better choice, hence the long-term solution. It requires no user intervention or reconfiguration to solve communication issues with the blocked SMTP port. To make the change permanent, just go to the SBC website and fill out an online form to unblock port 25.