Mails not downloading muiltiple clients

Hi,

I have multiple clients (outlook, ipad, android) which don't download consistently the emails from zoho.

I can see the webmails but not download.

On my android device I had to delete the account and add it using a different mail client (K9).

Is there something that changed a while ago that means the client won't download?

My account and that of my partner is the same and it appears to have been like this on and off for some time.

Please help.