DNN Websites have the ability to configure in the host settings an SMTP server. When a DNN email is generated from the DNN website, it will attempt to send mail through this SMTP server.
In order that your DNN website can successfully send the email, the SMTP server must allow the email message to be received. Typically this is done in one of four ways.
The SMTP server is configured for Open Relay (This should NEVER be done unless you have an external firewall blocking all external SMTP connections. Otherwise your mail server will become a spam server within hours)
SMTP Authentication – Typically SMTP servers are configured to allow users with a valid username and password to authenticate themselves. Once they have been authenticated, they can communicate email messages through the SMTP server. This is the same way most ISP’s work their mail servers. The idea is that only users who are customers of the ISP will allow email to be sent from their SMTP servers.
Selective Open Relay. The administrator of the SMTP server can also allow Open Relay (same as 1 above) from selective IP addresses. Any communication from an IP address that is configured to allow open relay will be accepted by the SMTP server.
Local Host – If your website has it’s own SMTP server configured, typically it will allow email message to be sent form it’s self.
To correctly configure your DNN SMTP settings, you need to understand what method of communication has been configured in the SMTP server you are trying to set DNN to access.
Here is the process you would configure from above.
Enter the IP address or valid domain name for the SMTP server, nothing more to do if open relay is allowed. (Still not recommended)
Enter the IP address or valid domain name for the SMTP server, and the valid user name and password as would be used to communicate with the SMTP server. This is where you get to use the user name and password setting in DNN.
Ensure that the SMTP administrator has allowed the IP address your DNN website uses to have open relay status. Then just enter the IP address or domain name of the SMTP server in your DNN host settings.
Configure your DNN host settings to have “localhost” in the DNN SMTP server settings are.
Problems. There can be some issues that get confusing with the different methods.
Open relay mail servers will be attacked by spammers very quickly. They are always on the lookout for mail servers that they can abuse. It is never recommended to have your mail server on the internet and in open relay. Additionally your mail server will be blacklisted by other mail servers if found to be in open relay.
SMTP Authentication can still be restricted to certain IP addresses. Many ISP’s will allow you only to use their mail servers while you are a client of their AND connecting to their mail server from an IP address they own. So thing will work in your Email applications while you are connecting to the internet via their dialup or high speed connection, but as soon as you move away from a connection provided by them, you will not be allows to connect to their servers, let alone Authenticate.
Even if your ISP has allowed relay from the address that your mail server is run form, there may be a firewall or block on the normal port that the SMTP servers are typically configured to use. Port 25. If a firewall exists between your web server and the mail server, it must be configured to allow traffic over port 25.
You may have web server configured with an SMTP server on the same system. Yet have it be blocked over port 25 for outbound communications. Some ISP’s block port 25 to curb the flow of virus email messages. You need to be sure that your ISP that provides connection to the internet for your web and SMTP server is not blocking port 25.
How to get really confused. Often mail servers will allow you to send email messages to email addresses on that SMTP server, even though they do not allow you to send mail out. So if you have a web application configured to send email to yourself, and the SMTP settings you use in the DNN host settings are for the SMTP server that runs the same email address you will have success. Yet when you change the email address in the web application, you can no longer send email, and the web application appears to fail. This is still an SMTP configuration error on your website. You will need to find a method above to solve the issue.