Emails Not Received From Website Form

I have just been through a frustrating experience where one of our clients suddenly stopped receiving email enquiries from their site. The website had been live for months and was built in ASP. The website has a number of enquiry forms on it which sends email enquiries directly to an email address of the client. The email address which received the enquiries is hosted on a different server to the website.

The website used CDOSYS to send emails; which is a built-in component within ASP which is used for the sending of emails. CDO (Collaboration Data Objects) is a technology from Microsoft designed to simplify the creation of messaging applications.

If you are looking for the code to for sending email with CDOSYS you can find it at w3scools.com.

So the story goes, one day I received an email from our client saying our email enquiries have stopped being received. This was a bit odd as we had not made any changes to the website code which would have caused this to happen. Our developers had performed a change the previous week so we investigated the code. We were puzzled as everything was working fine.

We created a test script to send an email using CDOSYS and the test email was received. Again when we checked our server logs we could see the emails from the forms were firing the emails correctly. We added a cc email to the website forms and ran some tests and these were all received fine.

It became clear the website code was not the culprit. We discovered it must be something else. We asked the company who managed the emails why their mail server was rejecting emails which were coming from the website. We asked them to white list emails from the site to allow them to come through but this still was not enough to get things working again.

They eventually came back to us to say the emails which were sent via the web server were being rejected by their spam filter. They uncovered the reason emails were not being received was because the IP address where the website was hosted was registered on the CBL.

CBL stands for composite block list. The CBL takes data from large spam traps and mail infrastructures and lists IP addresses which have been used to send spam, worms, viruses, etc. The CBL also lists Spam BOT and virus infecting download web sites, botnet infected machines, and other web sites or name servers dedicated to the use of botnets.

The CBL try to avoid listing IP addresses which represent shared hosting as there will be websites on the server being used for legitimate use. This was the case here; our client is on a shared host. The problem with shared hosting, whist it is much cheaper you can end up in a bad neighbourhood and it can affect you even when you have done nothing wrong.

It is easy to remove your IP from the CBL but if you delist your IP and the issue has not been sorted then you will reappear on the list within no time at all, which we discovered. As soon as we were delisted emails began filtering through again. However, within 24 hours the problem reoccurred.

Our server managers gave us a couple of options as to how we could quickly resolve this issue. The first was to update the script to send emails from a different SMTP server. Or we could move the site to a different server. We preferred the second option and overnight we moved to a different server. This gave the website a new IP address which is not on the CBL. Unfortunately there was nothing we could do to avoid this situation as the site is on shared hosting, but at least the problem has been resolved.