I’ve tested by editing file apps/mail/lib/Migration/MakeItineraryExtractorExecutable.php
and replaced line:
$this->logger->warning('itinerary file doesn\'t exist');
by:
$this->logger->warning('itinerary file doesn\'t exist: '.$this->file);
Then Log reader shows a more concrete message:
itinerary file doesn’t exist: /srv/www/dav.MyDomain.net/apps/mail/lib/Migration/…/…/vendor/christophwurst/kitinerary-bin/bin/kitinerary-extractor
I see that referred file really does not exist:
apps/mail/lib/Migration/…/…/vendor/christophwurst/kitinerary-bin/bin/kitinerary-extractor
but a different path yes, that exist located as:
apps/mail/lib/Migration/…/…/vendor/nextcloud/kitinerary-bin/bin/kitinerary-extractor
It seems a bug in “mail” application/extension files definition.