This update for claws-mail fixes the following issues:

- Update to 3.17.6:
 * It is now possible to 'Inherit Folder properties and processing
   rules from parent folder' when creating new folders with the
   move message and copy message dialogues.
 * A Phishing warning is now shown when copying a phishing URL, (in
   addition to clicking a phishing URL).
 * The progress window when importing an mbox file is now more
   responsive.
 * A warning dialogue is shown if the selected privacy system is
   'None' and automatic signing amd/or encrypting is enabled.
 * Python plugin: pkgconfig is now used to check for python2. This
   enables the Python plugin (which uses python2) to be built on
   newer systems which have both python2 and python3.
- CVE-2020-15917: Fixed an improper handling of suffix data after STARTTLS is mishandled (boo#1174457).

This update was imported from the openSUSE:Leap:15.2:Update update project.