Log Message:
Update to 2.4.0rc:

* The file copy and move were optimized.
* The crash on the cancellation of POP3/SMTP session was fixed.
* The crash when a person was removed and its e-mail addresses
  were referenced by a group in another folder was fixed.
* The Japanese manual was updated.

2.4.0beta8:

* In the address book, the import of CSV and Tab-separated text
  file was implemented.
* 'Within 1 day' and 'Recent 5 days' was added to the quick search rule.
* The toolbar style switch was added to the toolbar context menu.
* Stop button now cancels all sessions.
* The limitation of the nesting level of MIME structure was relaxed.
* A margin for text was added to the composition window.
* An error dialog is displayed if the execution of junk filter command fails.
* The overwrite confirmation of the file selection dialog was improved.
* ISO-8859-16 was supported in code conversion.
* Several UI problems in the address book were fixed.
* The stability of the cancellation of POP3/SMTP session was improved.
* The bug that the displayed number of message becoming incorrect on
  folder search was fixed.