...that you can go to the next and previous message by using the right and left arrow keys respectively?

...that you can rapidly create filters on sender, recipient, subject and mailing lists with Tools->Create Filter?

...that you can get rid of the "[mailing list name]" added to the subject of some mailing lists by using the rewrite header filter action? Just use

rewrite header "Subject"
   replace "\s*\[mailing list name\]\s*"
   with ""

...that you can associate mailing lists with folders in the Folder->Mailing List Management dialog? You can then use Message->New Message to Mailing List... to open the composer with the mailing list address preset. Alternatively, you can click with the middle mouse button on the folder.

...that you can assign custom icons to each folder individually? See Folder->Properties

...that KMail can show a color bar indicating the type of message (Plain text/HTML/OpenPGP) currently displayed?

This thwarts attempts to fake successful signature verification by sending HTML mails mimicking KMail's signature status frames.

...that you can filter on any header by simply entering its name in the first edit field of a search rule?

...that you can filter out HTML only messages with the rule

"Content-type" contains "text/html"?

...that when replying, only the selected part of the message is quoted?

If nothing is selected, the full message is quoted.

This even works with text of attachments when View->Attachments->Inline is selected.

This feature is available with all reply commands except Message->Reply Without Quote.

contributed by David F. Newman