If anyone is open to testing something, we have a version we just created that won’t use SMTP to send, but will use AirSync instead thus bypassing the issue altogether. You don’t need to change anything in eM Client except install this version, and you won’t need the registry workaround. You can remove that by using the removeoldoutlookcomflow.reg file on the Knowledgebase page or run the command for Mac users.
You can get the special version here for PC. Mac users can get it here. Please send any feedback to [email protected] regarding this version.