I have applications that as an example uses the email [email protected] (which is valid) to send email from, however lately users who fill out a webform online who use an external email(hotmail, gmail, yahoo) address do not receive email. I was able to resolve the issue by changing the outgoing mail sender to [email protected](this is an invalid email address). What causes this to happen? I apologize in advance if my question is too broad or not specific enough. I currently do not know enough about SMTP or network relays to explain more. Please note that this issue occurs on a server configured with IIS and one configured with apache.
2 Answers
1
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This article should solve your issue. (I know you didn't mention DotNetNuke, however I know your project and know you're utilizing it.)
DotNetNuke SMTP Configuration Requirements
You have four choices, each with a unique issue.
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.
1
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I think there is something else at play here. It doesn't make sense that mail would be delivered successfully with an invalid from address, but not with a valid from address. I would start be checking your mail server logs. These should show you whether or not receiving mail servers are accepting delivery of these messages from your mail server. If not, the logs may show you the reason that receiving mail servers are rejecting delivery.
The most likely causes of failed delivery are:
1) A DNS problem with your mail server. Check that your mail server is giving a correct name when it identifies itself in HELO or EHLO to other mail servers, and check that this name resolves to your mail server's IP, and that your mail server's IP reverses back to this name.
2) Your mail server's IP is blacklisted on one or more spam blacklists. You can check if your mail server is not listed on any blacklists at http://mxtoolbox.com/blacklists.aspx
