BCC header doesn't include the email when sending

Question

I'm seeing an issue of sorts in Mail.dll when comparing to Google at least.

I sent an email to two of my other email addresses using just BCC, no TO nor CC. I did it both with Mail.dll and then the same way using Google.

I noticed that with Mail.dll the BCC header is blank, while when sent from Gmail the TO header says undisclosed and the BCC has the email of the address I got the source.

Is that a bug of sorts?

Answer 1

This is not a bug.

Some mail clients send empty BCC to indicate there are Bcc recipients, some don't send BCC header at all.

In rare cases when a message is addressed to a single person, or the message is addressed to many addresses, but is send to each address individually, you can leave the BCC header containing the address of this single recipient - however I would advise against doing this.

You can easily add "Undisclosed recipients" group to the email's TO header:

MailBuilder builder = new MailBuilder();
builder.Text = "Plain text";
builder.From.Add(new MailBox("from@example.com"));

MailGroup undisclosed = new MailGroup("Undisclosed recipients");
builder.To.Add(undisclosed);

builder.Bcc.Add(new MailBox("bcc@example.com"));

var mail = builder.Create();

By default Mail.dll sends empty BCC header for emails that have Bcc recipients. It is possible to change that, but again I strongly advise against it, as you may reveal Bcc recipients by accident.