Bug #232: [STICKY] Annoying bugs in softwares used by DC
Webmail: cannot delete multi-page selection
If you select all mails in a box or through a search then deletion will only affect the current page; mails outside the visible page will not be affected. Selecting all mails without exception is working fine though.
See long-standing upstream bug: https://github.com/roundcube/roundcubemail/issues/5065