Not all emails being downloaded to Mac Mail

Does anyone else have this problem? Some, but not all, emails from my Zoho account are appearing in Apple Mail but it seems random, there doesn't seem to be any pattern. However they all seem to appear on my iPhone 5 using its mail program, and on my Surface 3 Pro tablet which uses Thunderbird. Does this mean that it's a problem with my iMac running Apple Mail (v8.2) on Yosemite? I've seen a whole heap of emails complaining about emails within Zoho disappearing etc. I don't have those problems, only this one

Does Zoho have a problem with Yosemite?

I've tried deleting the Zoho mailbox in Apple Mail and re-entering it but it made no difference. I followed Zoho's instruction page to the letter

The missing emails aren't in any spam folder that I can see, they just haven't been downloaded

I don't want to use Zoho as a standalone, although that would be a solution. I want to see emails from Zoho along with my other emails in Apple Mail from my other addresses, which are gmail, yahoo and hotmail. I have never had similar problems with any of these

Any help or suggestions would be very welcome.