Ongoing problems with Zoho mail

I'm relatively new to Zoho (about 6 mos). For the past 2 months all emails sent to my gmail, yahoo friends are either delayed or rejected. Although I see that Zoho reports this problem has been resolved, I just received yet another delivery "delay" notification for mail sent to a yahoo user.

Now, for the past 4 days, I've been having credential issues in Outlook, which is constantly prompting for my credentials. At first I thought it was Outlook (easy to blame them, they are usually the culprit :-), however, I tested on another mail client, having same problem there, but only for my zoho account. I've done considerable troubleshooting, including changing my password. Nothing solves the problem. Just this morning, started experiencing authentication issues on my iphone as well, again, only on zoho account.

Of course, I would love to get these issues resolved rather than go through the process of changing to another mail provider, but am starting to wonder if it wasn't a mistake to switch to Zoho. Is this kind of drama normal? Also, in reading many of the other forum posts, I see no support responses from Zoho people...is anyone out there? Or is this thing going down the tubes?