I am using the following code to send an email attachment. I’m using C#,

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Asked: May 23, 20262026-05-23T07:18:26+00:00 2026-05-23T07:18:26+00:00

I am using the following code to send an email attachment. I’m using C#,

0

I am using the following code to send an email attachment. I’m using C#, .NET 4.0, BPOS Exchange server to send.

var message = new MailMessage("duncanbayne@example.com", "duncanbayne@example.com")
    {
        Subject = "Test Message"
    };
var ms = new MemoryStream(Encoding.UTF8.GetBytes("我希望這個作品。"));
var attachment = new Attachment(ms, "檢", "text/plain")
        {
            TransferEncoding = TransferEncoding.Base64
        };
message.Attachments.Add(attachment);

var server = new SmtpClient("smtpserver", 25);
server.Send(message);

This works just fine. If I gradually increase the length of the filename, things continue to work, up to & including the point where the filename is 13 characters long (“檢檢檢檢檢檢檢檢檢檢檢檢檢”):

https://i.stack.imgur.com/lm1Ey.png

However, if I increase the filename length to 14 characters (“檢檢檢檢檢檢檢檢檢檢檢檢檢檢”), something goes awry and the filename appears in Outlook as though it’s been wrongly en/de-coded:

https://i.stack.imgur.com/gvNMV.png

In either case, the attachment contents are intact (“我希望這個作品。”). Only the name of the attachment is affected.

Clearly I’m hitting some sort of limit here … could someone please tell me what I’m doing wrong?

Update: The problem occurs regardless of whether the client is Gmail or Outlook 2010. However, when the client is Gmail and the filename is > 13 characters, the attachment also appears in the body of the message:

https://i.stack.imgur.com/DYtCN.png