Email gateways to CMSs have lots of great uses. From automating content creation from various sources, to allowing people out in the field to easily post from non-web enabled devices, or to just lowering the bar for getting content onto your site, email can be make content creation that much easier. Drupal has a number of options for incorporating email functionality- MailHandler is from my experience the best option to start with. On its own it offers a powerful functionality as a gateway. Unfortunately, for many users, learning the syntax for MailHandler is a bit of a barrier for its adoption for usage across the site. However, because of its accessible API, other modules have been built on top of it to provide additional services Mail2Web ups the ante by making it easy to keep threads going via email- essentially it provides mailing list like services for Drupal. For organizations who have users (like me) who refuse to migrate away from email, Mail2Web offers a great way to provide content on the site which mirrors email conversations. Using an Organic Group as the context for mail and web conversations from my vantage is the seamless extension of having threaded email/content functionality. Groups keep dialog located within a subset of users on the site. While Mail2Web uses Messaging and Notifications to do something approximating this, the ability to use the group context as as default context pushes functionality that much further. Enter Mail2Og which provides a very simple service- it maps an email-to address to a group title. This allows you to send an email a specific email address and have the content end up in the group context. For example, if you have a group named "My Super Duper Great Group", group members can email my_super_duper_great_group@domain.com and have the content auto posted to that group. With a simple catchall email alias accessed by mailhandler you can easily support all the groups on your site. You can also restrict this functionality per group as well. I wrote about this functionality over here.