The Problem (Q-score 8, ranked #220th of 303 in the Excel VBA archive)
The scenario as originally posted in 2012
I have an excel file (Excel 2003 / xls format) and I want to send it by email with c#.
My code send it successfully, but when I try to open the response file, it seems to encoded wrongly.
For example here is the response filename:
=_utf-8_B_RWxzesOhbW9sw6FzXzIwMTJfMTBfMTZf.dat
And here is the response file itself:
=?utf-8?B?VEdWdmJIWmhjMkZ1Wk1Pelh6UXlYekZmPz0NCiA9P3V0Zi04P0I/VGtW?=
=?utf-8?B?TlgwZFRXaTU0YkhNPT89?=” Content-Transfer-Encoding: base64
Content-Disposition: attachment0M8R4KGxGuEAAAAAAAAAAAAAAAAAAAAAPgADAP7/CQAGAAAAAAAAAAAAAAABAAAA
AQAAAAAAAAAAEAAAIwAAAAEAAAD+////AAAAAAAAAAD/////////////////////
////////////////////////////////////////////////////////////////
////////////////////////////// ….
Here is my code fragment:
...
var attachment = new Attachment(WriteFileToMemory("fileFullPath"), "fileName.xls");
attachment.ContentType = new ContentType("application/vnd.ms-excel");
attachmentCollection.Add(attachment);
...
private Stream WriteFileToMemory(string filePath)
{
var memoryStream = new MemoryStream();
_openedStreams.Add(memoryStream);
using (var file = new FileStream(filePath, FileMode.Open, FileAccess.Read))
{
var bytes = new byte[file.Length];
file.Read(bytes, 0, (int) file.Length);
memoryStream.Write(bytes, 0, (int) file.Length);
file.Close();
}
memoryStream.Position = 0;
return memoryStream;
}
How can I set the attachment encoding type, and which encoding should I use with Excel files?
Please help me solve this problem.
Thanks in advance.
Why community consensus is tight on this one
Across 303 Excel VBA entries in the archive, the accepted answer here holds niche answer (below median) status — meaning voters are unusually aligned on the right fix.
The Verified Solution — niche answer (below median) (+5)
6-line Excel VBA pattern (copy-ready)
You are making it too complex, as @Magnus points out, new Attachment() can handle FileStreams so just pass a new filestream to the constructor.
...
var attachment = new Attachment(File.Open("fileFullPath", FileMode.Open), "fileName.xls");
attachment.ContentType = new ContentType("application/vnd.ms-excel");
attachmentCollection.Add(attachment);
...
A word of warning though, kind is off topic, you cannot send a mail like that multiple times since the stream will not always reset itself properly.
When to Use It — vintage (14+ years old, pre-2013)
Ranked #220th in its category — specialized fit
This pattern sits in the 99% tail relative to the top answer. Reach for it when your scenario closely matches the question title; otherwise browse the Excel VBA archive for a higher-consensus alternative.
What changed between 2012 and 2026
The answer is 14 years old. The Excel VBA object model has been stable across Office 2013, 2016, 2019, 2021, 365, and 2024/2026 LTSC, so the pattern still compiles. Changes that might affect you: 64-bit API declarations (use PtrSafe), blocked macros in downloaded files (Mark-of-the-Web), and the shift toward Office Scripts for web-first workflows.