Krawler[x] comes equipped with its own Outlook-style personal message manager.
Click View » Personal Messages and select View Inbox to open the Messages tab in the Krawler Main Window. The panel on the left shows a tree-view of all the message folders.

The various message folders are Inbox, Outbox, Sent Items, Deleted Items, Drafts. Double-Click on any of them to view the messages stored in them.
At the top of the Messages tab there are buttons to do the following:
To send a personal message to a user, open his/her page and click the Send Message button at the top of the page. A New Message window will open where you can write your message. After writing the message and the subject, the Send button at the top-left corner of this window will become active, which you can then click to send your message.