Add (custom) headers to MailMessage class

Jan Reilink Code base

How to add custom headers to System.Net.Mail? When sending an email using the MailMessage class (System.Net.Mail namespace) in an ASP.NET website, certain email headers like Message-ID are not always set. When a Message-ID header is missing, email might be blocked by the recipients SMTP server like Gmail. Therefore it is necessary to set such headers.

Add custom header in MailMessage class / System.Net.Mail Namespace

The System.Net.Mail Namespace allows you to send authenticated SMTP email over TLS. Unfortunately, System.Net.Mail leaves out the mandatory Message-ID header. Here is how you can add this important header to your email. You can set a Message-ID, or any other custom header with the Message.Headers property and .Add method:

Message.Headers.Add( "Message-Id", "<" + Guid.NewGuid().ToString() + "@example.com>" );Code language: C# (cs)

Change example.com with your own domain name.

Custom headers
You can use this for other, custom headers as well, for example:

Message.Headers.Add( "X-Instance-ID", Convert.ToString( InstanceID[0] ) );Code language: C# (cs)

Related Posts

Share this post

Share on LinkedIn Share on Reddit

Jan Reilink

Hi, my name is Jan. I am not a hacker, coder, developer or guru. I am merely an application manager / systems administrator, doing my daily thing at Embrace - The Human Cloud. In the past I worked for clidn and Vevida. With over 20 years of experience, my specialties include Windows Server, IIS, Linux (CentOS, Debian), security, PHP, websites & optimization. I blog at https://www.saotn.org.