A class for sending emails with attachments in C#.

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Introduction

This is a SMTP client implementation in C#. It handles attachments and sending the body as HTML. It can also do basic (AUTH LOGIN PLAIN) and Base64 (AUTH LOGIN) authentication.

A little while back, I went looking for a (free) class/library to send email with in C#. I found several examples, but none fit my needs. They mostly demonstrated the basics and did not get into attachments. So, I decided to write my own implementation.

I reviewed several RFCs (821,822 mostly) and set about the task. The initial process was pretty straight forward and proved a good lesson in Tcp communication in C#. The attachment process was a little confusing. I understood how to do what I needed to, but was unsure of exactly what, and in what order, to do. The RFC for that and the MIME related ones aren't exactly crystal clear. That's when I found PJ Naughter's CSMTPConnection class. His implementation helped me to see the correct sequencing/structure of the MIME parts and was overall very useful. The version on The Code Project is a little old however, I would recommend getting it from PJ's site. Many thanks to him for a great example.

There is a second project in the solution which is a basic email form that uses this class.

The main class can be used as follows

Example usage of class:

SmtpEmailer emailer = new SmtpEmailer();
emailer.Host = "mymail.host.com";			
emailer.From = "someone@somwhere.com";
emailer.AuthenticationMode = AuthenticationType.Base64;
emailer.User = "myuserid";
emailer.Password = "mypassword";
emailer.Subject = "a test message";
emailer.Body = "this is only a test";
emailer.To.Add("toperson1@nowhere.com");
emailer.To.Add("toperson2@nowhere.com");
emailer.Attachments.Add(new SmtpAttachment(@"c:\file1.exe"));
emailer.Attachments.Add(new SmtpAttachment(@"c:\file2.txt"));      
emailer.SendMessage();

You can also send the body as HTML and include inline images by adding:

emailer.SendAsHTML = true;

When you send as HTML and you want to include images inline in the HTML, you would add the attachment as follows:

emailer.Attachments.Add(new SmtpAttachment(@"c:\mypicture.jpg", 
                        "image/jpg", AttachmentLocation.Inline));

The image will be given an ID that is it filename without extension. You then refer to the image in the html as

 <img src="cid:MY_FILENAME_WITHOUT_EXTENSION">

There is also an event, OnMailSent for use with the SendMessageAsync method. If people find this useful, then I will post updates/enhancements along the way. Enjoy.

Version History

1.4 - Added plain text (AUTH LOGIN PLAIN) and base64 (AUTH LOGIN) authentication.
Added CC/BCC properties.

1.3 - Fixed MIME header sequences and several issues with Outlook vs Outlook Express.

1.2 - Fixed quoted-printable encoding problem and an issue with Outlook.

1.1 - Added HTML body support, better MIME handling.

1.0 - Initial release.