Question

I am looking to have C# connect to an e-mail account and process undelivered mail or failures. And I would like the failed address or the original e-mail to be written to a text file.

I’m sure I could figure out how to identify failed message. Example: WHERE subject CONTAINS ‘failure’, ‘returned’, etc.

What I do not know how to do is collect the failed address from the e-mail.

I was using a program called popmonger for a client at one point, but now it is collecting the wrong e-mail addresses. It is collecting [e-mail] as an example instead of the original or failed e-mail. I thought it might be easier if I wrote a C# service.

The e-mail account I am connecting to is at hostgator. Does anyone know where to start on this?

Thanks,

Jake

Answer 1

Since the mail client being used is called popmonger, it sounds like you will be dealing with POP3 protocol and although .Net provides a way to send email via SMTP easily, it doesn’t really do the same justice when checking emails.

You will have to use a 3rd party DLL that has a POP3 client to retrieve the emails. Most importantly you will need to inspect one of the failure email notifications to see what what your application will be expecting. There should be something common in the subject, body, originator address, etc. to tip off which emails are failure notifications. Then you need to see where in the body of the email it specifies the error information you need to retrieve to write to the text file. Basically your steps should go something like this:

• Check for and retrieve email messages
• Add each failure email object to a collection (List<T> works just fine)
• Read/parse each email to extract the information you need
• Write the extracted data to a file
• As long as everything goes well and you get no exceptions, delete the email from the POP server with your POP client object (that way you don’t read the same failure notices every time and fill your text file with redundant data)

I’ve used a POP3 class from this codeproject article and it does include code for attachments but I never use it for attachments because it’s a bit buggy with them. For reading email body text, it hasn’t failed me yet (knocking on wood).

Once you have the failure notice you can extract the failed address per your prescribed format with a simple regular expression pattern and matching it. Let’s assume the body text is already retrieved from the server and you stored it in a stringed named bodyText

using System.Text.RegularExpressions;
// ...

string failedAddressPattern = @"The mail system <(?<address>.+)>";
string capturedAddress = null;
Match match = Regex.Match(bodyText, failedAddressPattern, RegexOptions.IgnoreCase);

if(match.Groups["address"].Success)
{
    capturedAddress = match.Groups["address"].Value.Trim();
}

if(capturedAddress == null)
{
    // do some form of debug logging here because the pattern no longer works, etc.
}