Why do emails arrive so late?

Why do emails arrive so late?

I'm forwarding emails from gmail to zoho. They arrive in my zoho inbox up to 2 hours later than they are forwarded from gmail.

This is not a problem with gmail, I've forwarded elsewhere and they arrive right away. Only with zoho do they take forever to arrive....

This happens with about 50% of my incoming emails. I won't give specific email IDs, it's a prevalent issue.