What is the use of IMAP in ps 1.7's customer support?

[Vailry]

I've upgraded my zoho account to be able to use imap. Imap is installed on my upuntu 16 server with php 7.1. I can use the zoho account flawlessly via thunderbird and prestashop is connected to it. Syncinc works fine and as of now it gives me the "NO message to sync" message. 

 

However, neither my replies to customers get sent, nor do the e-mails from customers actually get forwarded to the in contacts stated e-mail addresses.