System.Net.Mail and =?utf-8?B?XXXXX.... Headers

Question

I'm trying to use the code below to send messages via System.Net.Mail and am sometimes getting subjects like '=?utf-8?B?W3AxM25dIEZpbGV...' (trimmed). This is the code that's called:

MailMessage message = new MailMessage()
{
    From = new MailAddress("[email protected]", "Service"),
    BodyEncoding = Encoding.UTF8,
    Body = body,
    IsBodyHtml = true,
    ReplyTo = new MailAddress("[email protected]"),
    SubjectEncoding = Encoding.UTF8
};

foreach (string emailAddress in addresses)
{
    message.To.Add(new MailAddress(emailAddress.Trim(), "Person"));
}

message.Subject = subject;

I'd like to emphasize that this does not happen all of the time.

What am I doing wrong?

Answer 1

When your subject contains characters outside the ASCII range, then the mailing software must encode them (RFC2822 mail does not permit non-ASCII characters in headers). There are two ways to do this:

• Quoted Printable (subject starts with "=?utf-8?Q")
• Base64 (subject starts with "=?utf-8?B")

It appears that the framework has figured that the Base64 encoding is more efficient (=shorter) than the quoted-printable encoding. This makes sense when your subject contains relatively many characters outside the ASCII range.

To answer your question: You're doing nothing wrong. That's how internet mail with non-ASCII characters is supposed to look like. Of course, the software that reads such mail should detect and decode such subject fields.