Managing Delay in emails

==== Required information ====
- iRedMail version: v0.2
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):  MySQL
- Linux/BSD distribution name and version:  Linux(CentOS)
- Related log if you're reporting an issue:
====

I want to manage delay in receiving and sanding emails, i.e Can i add trusted domains/IPs in grayscale ?  and block domains/IPs if So please guide me.

Best Regards,
Waseem Hassan