Cannot open saved zip files extracted from Outlook Mail via C#

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.NET3.5

Hi Everyone,

I've created a small C# application which extracts attachments from outlook emails and saves them to a network location. I can open all of the saved files except for compressed files with "zip" extension.

Files with the "zip" extension can only be opened/extracted via Windows Explorer. If I try to use WinRAR, I get the following error: "The archive is either in unknown format or damaged". WinZip does not work either. If however, I open the email within outlook manually and copy the zip file to my PC, I am able to open the zipped file using WinRAR, WinZip as well as windows explorer.

Part of the code used to save the attachment is shown below.

        Microsoft.Office.Interop.Outlook.MailItem _mailItem;<br />
        ...<br />
        ...       <br />
        _AttachFileName = _mailItem.Attachments[j].FileName;<br />
        _TempAttachmentFile = Path.Combine(_tempFolder.Path, _AttachFileName);<br />
<br />
        _mailItem.Attachments[j].SaveAsFile(_TempAttachmentFile);<br />
        ...<br />
        ...

Has anyone faced a similar issue with compressed zip files? If so were you able to resolve the issue?

Any ideas or help on this will be appreciated.

Thanks
Navnit

Posted 11-May-11 16:07pm

CoolFijiKid

Updated 11-May-11 16:09pm

v2

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CS2011 11-May-11 22:48pm

Can you post what is the error message you are getting ?

CoolFijiKid 11-May-11 23:51pm

WinRAR error:
"The archive is either in unknown format or damaged"

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Manish Ranjan Kumar · Answer 1 · 2011-05-11T17:05:00

This is the peace of code i tried which works fine.

Can you please test it.

Application app = new Application();
            NameSpace nameSpace = app.GetNamespace("mapi");
            MAPIFolder defaultFolder = nameSpace.GetDefaultFolder(OlDefaultFolders.olFolderSentMail);
            foreach (MailItem item in defaultFolder.Items)
            {
                foreach (Attachment att in item.Attachments)
                {
                    if (att.FileName.EndsWith("zip", StringComparison.CurrentCultureIgnoreCase))
                    {
                        att.SaveAsFile(Path.Combine("c:\\delete me", att.FileName));
                        break;
                    }
                }
            }
            app.Quit();

Sergey Alexandrovich Kryukov · Answer 2 · 2011-05-11T16:59:00

How do you know it is a valid e-mail?
What happens if you save whole e-mail in a file, name is as *.eml and open in Outlook Express (bundled with all Windows versions)? Can you save and open binary files from e-mail sections.

Open the file with text editor. Even if the e-mail contains binary files, it's always a plain text file. You should see it content type "Content-Type: multipart/alternative", in case of zip your binary section should be a part with

Content-Type: application/octet-stream; name="yourfilename.zip"
Content-Disposition: attachment; filename="yourfilename.zip"
Content-Transfer-Encoding: base64

These line must be followed by an empty line followed by base64-encoded string. You should be able extract it manually and decode using System.Convert.FromBase64String.

Do you see something like that?

Look how processing of attachment is implemented here:
A POP3 Client in C# .NET[^] (it's about POP3, but you're interested only in the the structure of e-mail).

—SA

CoolFijiKid · Answer 3 · 2011-05-11T17:46:00

Hi Everyone,

Thanks for providing suggestions for my issue. I managed to get to the bottom of the issue. The problem I was having wasn't caused by the code I posted earlier.

After posting my issue on the forum, I had a closer look at what I was doing within my code and found that at a later stage of my application code, I was converting the attachment into base64 string for some internal processing. This was eventually getting saved back as a file to the final destination folder. It was during this final saving process I accidently reduced the data by a byte.

Code causing the issue:

<br />
FileStream outFile; <br />
..<br />
outFile.Write(binaryData, 0, binaryData.Length-1);<br />
..<br />

Fixed code:

<br />
FileStream outFile; <br />
..<br />
outFile.Write(binaryData, 0, binaryData.Length);<br />
..<br />

Apologies for the confusion.

Cannot open saved zip files extracted from Outlook Mail via C#

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