paulmac

WordPress allows posting via email, but must be told to check for emails. This is achieved by calling wp-mail.php using either a cron job, or by including a hidden iframe in your blog footer.
This plugin adds the iframe to the blog footer without editing the theme – updating your theme won’t break your ability to email in posts to WordPress.

Email Post Activation

Adds an iFrame to your blog footer to automatically activate any posts written by email.

Andy Peatling

techguy

Disables the activation email and automatically activates new users in BuddyPress under a standard WP install and WPMU (multisite). Also, automatically logs in the new user since the account is already active.
Possible Future Features: 
-Option to turn off automatic login 
-Option to not disable email 
-Redirect options after account creation
Known Bugs: 
-Doesn’t do the automatic login if you allow blog creation during the user creation in WPMU (multisite)

BP Disable Activation

Disables the activation email and automatically activates new users in BuddyPress under a standard WP install and WPMU (multisite).

Email Post Activation vs BP Disable Activation