Email missing on exchange client

Email missing on exchange client

Hi, I'm trying out zoho at the moment and I'm having a little problem with exchange/activesync.

I received some emails from amazon which were immediately sent to the spam folder (I've now changed my spam settings).  When I marked them as not spam in Zoho Mail they were moved back into my inbox, however they are not getting synced to my mobile device which is using exchange.  All other changes to my inbox are reflected on my phone apart from these emails.

Does anyone know why and how to rectify it?

Thanks in advance