How can you set the SMTP envelope MAIL FROM using System.Net.Mail?

Question

When you send an email using C# and the System.Net.Mail namespace, you can set the "From" and "Sender" properties on the MailMessage object, but neither of these allows you to make the MAIL FROM and the from address that goes into the DATA section different from each other. MAIL FROM gets set to the "From" property value, and if you set "Sender" it only adds another header field in the DATA section. This results in "From [email protected] on behalf of [email protected]", which is not what you want. Am I missing something?

The use case is controlling the NDR destination for newsletters, etc., that are sent on behalf of someone else.

I am currently using aspNetEmail instead of System.Net.Mail, since it allows me to do this properly (like most other SMTP libraries). With aspNetEmail, this is accomplished using the EmailMessage.ReversePath property.

Answer 1

MailMessage.Sender will always insert a Sender header (interpreted as on behalf of in your e-mail client).

If you use the Network delivery method on the SmtpClient, .Sender will also change the sender in the envelope. Using the PickupDirectoryFromIis delivery method will leave it to IIS to determine the envelope sender, and IIS will use the From address, not the Sender address.

There's a similar question on MSDN here.

Answer 2

I just found how to do it:

• mail.From specify the email from visible to the final user
• mail.Sender specifies the envelope MAIL FROM

That's it (even if it took me a while to figure it out)