It may not make sense it man but my self and the other 3 techs have fielded over 50 calls from clients on Eset with this exact issue wince ver 14. and the work around I explained is the solution every single time.
Thunderbird does not suffer from these issues, Eset seems to handle its integration with the mail servers automatically and its working as intended.
This is an eset with outlook issue, I've confirmed it on outlook 2013, 2016 and Outlook 365. None of our clients who use Thunderbird have issues.