Mail not received chronologically

Mail not received chronologically

This is not a huge issue.  But it's weird.

Sometimes I get morning mail in the afternoon - and it's slipped into it's regular time slot in the email list.

For example, I'll review and mark all my email as 'read' from the morning.  Then some hours later, I'll see unread mail slipped in around the morning time frames.

Is this a Zoho thing?  Why would some emails not be received for hours after their time-stamp?