php-mapi: research problems with retrieving html from emails and resolving recipients

https://forum.kopano.io/topic/296/bugreport-kc-8-4-0-667_139-error-while-accessing-html-mail-items-in-webapp

"could not open message" for html mails reported on:
CentOS 6.9
PHP-FPM 5.6.30
Core 8.4.0~667
Webapp 3.4.0.676 or 3.4.0.670
rolling back to core-8.4.0~644_137 restored functionality

Ubuntu 14_04
KopanoCore 8.4.0.669
Webapp 3.3.0.610-25.1 or Webapp 3.4.0.676

Ubuntu 16.04
Core 8.4.0-728
WebApp 3.4.0.686-479.1
php-fpm (PHP 7.0)
(z-push shows user himself as sender)

https://forum.kopano.io/topic/321/incident-no-sender-on-iphones-since-latest-kopano-update

no sender information synced to z-push reported on:
Ubuntu 16.04.2 LTS
Apache 2.4.18
Z-Push 2.3.6
Kopano 8.4.0-728
was running 8.4.0-553 before

https://forum.kopano.io/topic/315/kopano-core-8-4-0-sender-problems-after-upgrade
some e-mails show no sender at all as well as on WebApp and on mobile devices (iOS
Some mails won’t open on WebApp (failed to open Dialog)
and I can not use the reply-to feature in any mail (empty recipient when editting mail)
upon upgrade from 8.3.0~667 to 8.4.0~728

https://forum.kopano.io/topic/328/send-as-not-work
send-as not working
when using send-as the dagent responds with a message that the user or group does not exist
used 8.4.0-693 and afterwards downgraded to 8.4.0-35 (as stated in https://forum.kopano.io/topic/327/kopano-core-rollback)

https://forum.kopano.io/topic/325/e-mail-answer-to-field-empty
to field empty on email answer
same user as "send-as not working"
Core 8.4.0~728_144.1 and Webapp 3.4.0.686_479

https://forum.kopano.io/topic/301/error-could-not-resolve-user
Error Could not resolve user.
Debian 7 x64
WebApp: 3.4.0.676-474.1
Kopano Core: 8.4.0-667
says that dropping the database and reimporting with kopano-backup resolved the issue (https://forum.kopano.io/topic/301/error-could-not-resolve-user/4) (but also installed an older version)

not affected:
core-8.4.0~644_137
8.4.0-553
8.4.0-465
8.4.0-415
8.4.0-35
8*.3.*0~667