Using todays core-18.104.22.1681 (also 22.214.171.1240 from Monday), Umlauts are broken in the subject line of sent mails.
I initially thought someone broke Outlook 2010 support unintentionally, but this is also present without using Outlook 2010.
- Mail sent from external Kopano (126.96.36.1991) Outlook 2010 to me (different Kopano 188.8.131.521 system): broken in IMAP (Thunderbird) and Outlook 2016
- Mail sent from my own Outlook 2016 to myself: ok in Outlook 2016, but not ok in WebApp and IMAP (Thunderbird)
- Mail sent from Outlook 2010 to myself (Outlook 2010): broken
Here are two screenshots from Thunderbird and WebApp how it looks. The word should correctly be shown as “Geschäftsbericht”.