A GREYLIST is useful to bypass SBRS filtering for a specific host, in the case the host name or sending MTA may encompass other senders other than your specific trusted user. When using this GREYLIST, the mail is still scanned for SPAM which differs from using the ALLOWLIST which bypasses SPAM scanning.
To setup a GREYLIST in the GUI:
Navigate to GUI > Mail Policies -> HAT Overview -> Add Sender Group.
Name the group GREYLIST and select an order of "1".
Choose the "ACCEPTED" mail flow policy.
Leave all other settings at their defaults.
Click Submit and Add Senders.
Enter the IP address or hostname of the sender.
Submit this page.
If needed, click Add Sender and keep adding any additional IP addresses.