Latency in receiving mail

Latency in receiving mail

I have created zoho mail for my office. Initially I have added 3 users alone. Every one has problem in receiving emails. It takes 1 to 3 hours to receive mails sent from other colleagues. 

All your features are amazing, but everyone is disappointed with latency in email receiving.  Please look into this issue, so that we could create zoho mails for our entire office.