I host Ex13, and somehow the connector has gone wonky. Shared calendars work fine in OWA, but Outlook clients get repeated password prompts and posts don’t get published. Was a working environment for years til this hiccup. If you close all shared calendars, the prompts for password stop. Email flow is fine though.
Outlook connections off domain are working. It seems to be an issue with what server name? But I’ve followed the online guides, and tried using URI/URL’s with both the correct ext/int names, and tried using just the external names. Neither seem to resolve the issue for domain machines on domain