Push not working for IMAP using K9 Mail on Android

Hello,

I am having issues getting 'Push' to work in combination with an IMAP email account using K9 Mail on Android. When I select Push instead of Poll, no messages are retrieved. Instead, I have to actively poll the server every X minutes for it to retrieve mail. Is anyone else experiencing issues with Push and IMAP not working?

I am running SmarterMail 16.3.6663 on Windows Server 2016 in combination with K9 Mail 5.403 on Android 6.0.1

Thank you