<p>My company runs a webmail service, and we were trying to diagnose a problem with Word downloads not opening automatically - the same *.doc file download from Yahoo Mail would open, but one from ours would not.</p>

<p>In the course of investigating the headers we saw this coming from Yahoo:</p>

<pre><code>content-disposition attachment; filename*="utf-8''word document.doc";
</code></pre>

<p>Whereas our headers were like this:</p>

<pre><code>content-disposition attachment; filename="word document.doc";
</code></pre>

<p>What exactly is Yahoo doing with the additional asterisk and utf-8'' designation?</p>

What Mime-Type are you using?
The asterisk is required as per RFC 2183 (
http://www.ietf.org/rfc/rfc2183.txt
):
In the extended BNF notation of [RFC 822], the Content-Disposition
   header field is defined as follows:
```
```
disposition := "Content-Disposition" ":"
                disposition-type
                *(";" disposition-parm)

 disposition-type := "inline"
                   / "attachment"
                   / extension-token
                   ; values are not case-sensitive

 disposition-parm := filename-parm
                   / creation-date-parm
                   / modification-date-parm
                   / read-date-parm
                   / size-parm
                   / parameter

 filename-parm := "filename" "=" value

 creation-date-parm := "creation-date" "=" quoted-date-time

 modification-date-parm := "modification-date" "=" quoted-date-time

 read-date-parm := "read-date" "=" quoted-date-time

 size-parm := "size" "=" 1*DIGIT

 quoted-date-time := quoted-string
                  ; contents MUST be an RFC 822 `date-time'
                  ; numeric timezones (+HHMM or -HHMM) MUST be used
```
```