Email connection with my own domain

I've been trying for the last few days every email client I could find to get a stable connection with server imappro.zoho.com, and finally it occurred to me it might be the server's fault.

I'm using iMac on Sierra. With every mail client, everything looks fine after the setup, I'm getting emails sent out, and receiving emails fine. Then I leave the mail client open for a while, I start to get login errors from zoho error, I could make it right by putting the password again. The only way to stop that error is either to choose cancel on the error window, or restart the mail client. Then it'll still work fine for a while before the error starts again. Every mail client I've tried is the same, until thunderbird took it upon itself to set the server to imap.zoho.com, which worked all good for the whole day. That's why I think it might have something to do with the new imap server.

Having said that, both the apple mail client on my IPhone, and the gmail client on my android phone work all right without a fail. And the server is set to imappro.zoho.com.

Please help. I don't think I can use imap.zoho.com for ever.