email sync only 99% to CRM

Hey guys.

i receive approximately 300 emails per day, in a mailbox configured with server-side Sync, with Exchange. 99,9% of the times the emails are integrated on CRM, but i'm noticing some emails aren't, with no apparent reason.

i don't see any errors in the mail configuration/etc, is there any way to ensure that all emails that arrive at Exchange mailbox are integrated? where should i look for a reason for this to happen?

I'm using CRM 2013 on-premises, with SP1 w/ UR1.

Thanks in advance,

Regards,

approximately