private 

Author: Rilwis This plugin allows users of WordPress blog send private messages (PM) to each other. The number of PM can be controlled in plugin option page
Installation:
Unzip downloaded file and upload folder pm4wp to the /wp-content/plugins/ directory Activate the plugin through the Plugins menu in WordPress Set the number of PM for each user role in the plugin option page (or you can use the default option) Set how to choose recipient: from dropdown list or auto suggest from user input Now you will see a new menu Messages in the left. Just select Send for sending PM or check the Inbox and Outbox.
faq:
How can I set the number of private messages for each user? You can set number of PM for only user role (group): Administrator, Editor, Author, Contributor, Subscriber. The option is in the plugin option page (Settings > Private Messages) How can I delete my old PM? Go to Inbox or Outbox, and click the link Delete after each message to delete it. Or you can check multiple messages and select Delete action from the dropdown box. How can I reply to sender? Just click the Reply link below the message in your Inbox. What can I do if I exceed my limit? You can delete your old PM (see previous question) or ask admin to increase the mailbox quota. Other questions? More screenshots? Please visit the homepage for Private Messages For WordPress.

Authors: kilotto, fulippo, kifulab Wp Private Access adds an http authentication dialog using WordPress users database. Wp private is particularly useful for testing blogs and websites based on WordPres
Installation:
Upload the Wp Private Access plugin to your blog, Activate it. Enjoy ;)

Author: Rilwis This plugin allows users of WordPress blog send private messages (PM) to each other. The number of PM can be controlled in plugin option page
Installation:
Unzip downloaded file and upload pm4wp.php to the /wp-content/plugins/ directory Activate the plugin through the Plugins menu in WordPress Set the number of PM for each user role in the plugin option page (or you can use the default option) Now you will see a new menu Messages in the left. Just select Send for sending PM or check the Inbox and Outbox.
faq:
How can I set the number of private messages for each user? You can set number of PM for only user role (group): Administrator, Editor, Author, Constributor, Subscriber. The option is in the plugin option page (Settings > Private Messages) How can I delete my old PM? Go to Inbox or Outbox, and click the link Delete after each message to delete it. Or you can check multiple messages and select Delete action from the dropdown box. How can I reply to sender? Just click the Reply link below the message in your Inbox. What can I do if I exceed my limit? You can delete your old PM (see previous question) or ask admin to increase the mailbox quota. Other questions? More screenshots? Please visit the homepage for Private Messages For WordPress.

Author: Rilwis This plugin allows users of WordPress blog send private messages (PM) to each other. The number of PM can be controlled in plugin option page
Installation:
Upload pm4wp.php to the /wp-content/plugins/ directory Activate the plugin through the Plugins menu in WordPress Set the number of PM for each user role in the plugin option page (or you can use the default option) Now you will see a new menu Messages in the left. Just select Send for sending PM or check the Inbox and Outbox.
faq:
How can I set the number of private messages for each user? You can set number of PM for only user role (group): Administrator, Editor, Author, Constributor, Subscriber. The option is in the plugin option page (Options > Private Messages) How can I delete my old PM? Go to Inbox or Outbox, and click the link Delete after each message to delete it. Or you can check multiple messages and select Delete action from the dropdown box. How can I reply to sender? Just click the Reply link below the message in your Inbox. What can I do if I exceed my limit? You can delete your old PM (see previous question) or ask admin to increase the mailbox quota.