Sync.zoho.com seems not working well on Outlook

Sync.zoho.com seems not working well on Outlook

Hello,
it's few days that on my Outlook client the sync with Zoho Mail doesn't work well, as it doesn't dowlonad ALL the emails, but just few.
If I delete the account on my Outlook and then I create it again the sync is ok, but after few minutes all the email downloaded disappear and it start to sync agin but just the last ones.
What is it happening?

Thanks

Max