unable to encode special characters email in right format, gmail api & ae.net.mail

Question

I'm working on an application that can send emails out with attachments and it works, until I try special characters æ, ø, å.

I played a bit around testing different encodings and it looks like the subject is being encoded in ISO-8859-1 while the rest of the mail is encoded in UTF-8.

Here is my method that generates a Google Gmail API message

        public Message CreateMessage(string to, string from, string body, string subject, GmailService service, string[] files = null, string bcc = null)
    {
        AE.Net.Mail.MailMessage message = new AE.Net.Mail.MailMessage()
        {
            Subject = subject,
            Body = body,
            From = new MailAddress(from),
        };

        message.To.Add(new MailAddress(to));
        message.ReplyTo.Add(message.From);

        message.Headers.Add("Content-Type", "text/plain; charset=utf-8");

        if (bcc != null)
            message.Bcc.Add(new MailAddress(bcc));

        if (files != null)
        {
            foreach(string file in files)
            {
                using (var opennedFile = File.Open(file, FileMode.Open, FileAccess.Read))
                using (MemoryStream stream = new MemoryStream())
                {
                    string[] FileName = file.Split('\\');
                    opennedFile.CopyTo(stream);
                    message.Attachments.Add(new AE.Net.Mail.Attachment(stream.ToArray(), MediaTypeNames.Application.Octet, FileName[FileName.Length - 1], true));
                }
            }
        }

        var msgStr = new StringWriter();
        message.Save(msgStr);

        return new Message() {
            Raw = Base64UrlEncode(msgStr.ToString()),
        };
    }

    private static string Base64UrlEncode(string message)
    {
        var inputBytes = Encoding.GetEncoding("utf-8").GetBytes(message);
        return Convert.ToBase64String(inputBytes).Replace('+', '-').Replace('/', '_').Replace("=", "");
    }

message.ContentType = "text/plain; charset=utf-8" does not fix this issue and makes the attached files show in the body as Base64

Answer 1

You could use the following technique to use UTF-8 in the subject header.

=?charset?encoding?encoded-text?=

You could then use charset=utf-8, encoding=B (B = base64), and encoded subject as encoded-text.

Example

Subject: =?utf-8?B?aGVsbG8=?= // 'aGVsbG8=' is 'hello' in base64 format.