You have the basics down, but this is a bit too early for a review.

I will say to make sure you're following pep8 conventions with spacing between imports and the class.

Looks like a decent start. I want to figure out what the plan is going forward, though.

Is the idea to have one e-mail that goes out to everyone, or to have e-mails, say, per-person? If so, these queries are going to change. If it's for everyone, then that's fine for tiny installs, but won't scale up to organizations of thousands of people (most of whom don't care about anybody outside their immediate group).

So maybe make this flexible. Take some parameters for specifying one or more group names (and use those in the queries), or usernames. The output should be customized based on those parameters.

Look at reviews/managers.py for various query options. You'll want to use these because they take into account LocalSites (which are very important -- an installation with LocalSites must never see info on each other).

Two blank lines.

Comments must always be in sentence form.

Blank lines around each loop or other block.

Basic rule: If there's code before/after an if statement or loop on the same indentation level, use a blank line to separate them.

Keep lines under 80 characters

Missing whitespace after the "," in lambda, and also after the ":" right after lambda

Only one space after the second ","