Xobni puts a ton of social info in an Outlook sidebar.

It's important to know who you're talking to. But in our e-mail in-boxes, we're deluged with messages from people we don't know, companies we're not familiar with. Even messages from our friends and coworkers could be better handled if we had social or business context with the message.

To see what I mean, try at least one of the these three good tools: Xobni, Rapportive, and a new kid on the block, WhoSent.It. These tools all give you dossiers on the people e-mailing you by using data gleaned from around the Web, including Facebook profiles, Twitter postings, and, for business users, data from apps like Salesforce.com.

Of these apps, Xobni is for Outlook users. Rapportive works nicely with Gmail and Google Apps. WhoSent.It has a clever twist that makes it work with anything.

If you're an Outlook user, get Xobni. Like the other apps, it pulls personal data from Facebook, Twitter, and Linked in, and company data from Hoovers. Xobni also gives you relevant data from within your own e-mail archive: It gives you links to e-mails you've exchanged with the sender, and also shows you which other people the sender communicates with (taken from multi-addressed to: and cc: fields). Xobni's sidebar data panel looks great and is the front-end for a ton of additional info, though on a crowded notebook's screen it can be a little intrusive.

Rapportive replaces Gmail&39's ads with a useful info pane.

Rapportive works with Gmail and its corporate cousin, Google Apps. Primarily it grabs data from the usual suspects of social sources: Facebook, Twitter, and LinkedIn. Users can also connect Rapportive to less universally used lookup tools, like Klout, Lanyrd, and Crunchbase. Rapportive's benefit is its easy setup--it's a browser plug-in--and, thanks to its cloud architecture, its minimal drag on the user's computer. It's a no-brainer if you use Gmail, although in my tests it did fail to pick up social profiles from some people I know I'm connected to.

Rahul Vohra, CEO of Rapportive, told me a Xobni-like history section will be added to his service soon.

Then there's the new app, WhoSent.It. Very much a work in progress, this dossier utility works with any e-mail system through a clever routing hack: When you want to look someone up in the free version, you forward the message from them to who@whosent.it. The service reads the e-mail, and you get a dossier page back with details on the person. Alternatively, enterprise users can route all their incoming e-mails through WhoSent.It, to get the dossiers appended to messages.

WhoSent.It sends you an e-mail dossier when you forward it messages. It still needs some development.

WhoSent.It does need to grow up a bit before I can recommend it, but hopefully this will happen soon. It doesn't return much information, even when you connect it to your Facebook account, and in my testing it also got some info oddly wrong (my father is not female). But WhoSent.It is launching with the capability to pull data from Salesforce.com and Jigsaw, which is useful to businesses. And it's the only service you can start using immediately from a smartphone, if you need a quick bit of info on someone and you're not near your desktop.

The CEOs of all of the dossier apps told me they're big into mobile. At the moment, WhoSent.It works with any platform, so it's probably the best bet for getting info on a contact when you're not at your desk--and you're not an Outlook and BlackBerry user, since Xobni has a BlackBerry app (review). Rapportive's Vohra says mobile support is in the pipeline for that app.

There are free versions of each of these services, with up-sells for premium features. Either Rapportive or Xobni will instantly give you social context that your e-mail in-box is currently lacking. And WhoSent.It has potential--watch for it to improve.