In the meantime, we can suggest the following workarounds: Our Development team is working on a permanent solution under issue ID CONNECT-94898. Since its release on, there have been a number of reports of this formatting issue occurring with Outlook version 2205, which were not occurring for the same users previously. If you are on any version previous to the one mentioned above, it is likely a compatibility issue between MAPI and HTML formatting.If you are on version 2205 (Build 15225.20204) or newer of Outlook, please refer to Solution A below.
The likelihood of each root cause depends on the version of Outlook you are running. This article provides the possible root causes and suggested workarounds. It has been reported that HTML formatted emails are displayed in plain text in Kerio Outlook Connector (Offline Edition) (KOFF).