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Yahoo Mail not decoding base64 PDF attachment RRS feed

  • Question

  • I've run into an issue recently with a asp.net (vb) application I use to send email with PDF attachments. Yahoo Mail users periodically (but not always) are not able to view or download PDF attachments that we send ever since we upgraded from .Net 3.5 to .Net 4.0.

    More specifically, Yahoo Mail downloads the attachment as a text file containing the base64 content, and with the correct filename, rather than the decoding the file. This isn't an issue for any other email client, gmail, hotmail, etc. as far as I know; only Yahoo.

    We're using a standard .Net MailMessage, an exchange 2010 server, and attaching from a file (or a stream).

    The raw body of the email looks the same between the two .Net versions except that .Net 4 adds the line
    Content-Disposition(colon) attachment

    before the beginning of the Base64 encoded text.

    I've tried manipulating all the SMTP headers I can think of with no luck; and I'm at a bit of a loss as to what to try.



    • Edited by heh3d Monday, March 24, 2014 9:41 PM
    Monday, March 24, 2014 9:39 PM

Answers