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Asked: 2026-05-11T04:20:12+00:00

I’m trying to use the code below to send messages via System.Net.Mail and am

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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('someone@somewhere.com', 'Service'),     BodyEncoding = Encoding.UTF8,     Body = body,     IsBodyHtml = true,     ReplyTo = new MailAddress('do.not.reply@somewhere.com'),     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?

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1 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.

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