| is Yahoo Mail really in such a bad place that
  | they need to outsource their file attachment
  | hosting?

I imagine that Yahoo! Mail is similar to Gmail in that there are size limits on the emails that you can send. Your email with attachments can't be over 20 ~ 25Mb on Gmail. I think that Hotmail's limit is around 10MB. Partnering with Dropbox would allow one to use their Dropbox space for much larger files.

  | When I'm using outlook, I click on a file once
  | and it downloads, simple as that, I don't want
  | to have to screw around signing up for yet another
  | service just to use it.

Dropbox allows you to share files publicly, IIRC. They could take this a couple of ways:

- When attaching, the user could be presented with a dialog that allows them to select files already in their Dropbox account. Therefore if you wanted to upload a file, you could drop it into your Dropbox folder, then compose an email.

- When attaching, the user uploads the file to their Dropbox account via the Yahoo! Mail web interface.

Both of these ways will probably create a URL to the file on Dropbox (publicly accessible, private with password, obfuscated single-use URL, etc).

[ Also, we're talking about webmail clients like Yahoo/Gmail/Hotmail. It really seems like you're comparing them to Outlook+Exchange, which is something completely different. ]

There are three integration points:

- Share from Dropbox: when composing an email, insert a link to a file already in your Dropbox.

- Save to Dropbox: when reading email, save a received attachment to your Dropbox.

- Upload to Dropbox: if you try to attach file over the 25MB attachment size limit, you're given the option to upload it to your Dropbox and link to the file on Dropbox.

All major email providers have pretty low size limits for their email attachments. I believe Hotmail/Outlook uses Skydrive to attach files over 10Mb. Since, Yahoo doesn't have Yahoo Drive they partnered with Dropbox to do the same thing. It seems like a good move to me; get closer to functional parity with your competitors and utilize a very popular file syncing solution.

> is Yahoo Mail really in such a bad place that they need to outsource their file attachment hosting?

More likely they're in a place where they'd like the referral revenue that's likely involved if/when those users upgrade to a paid Dropbox account.

Having attachments available across computers/mobile devices can in some cases be a huge win.

I can see it being a disaster in some cases, but I see it as a huge plus in another section.

Dropbox is just about ubiquitous enough for this to be useful.