Whitelist IP(s) Used for Zoho Mail Webmail

Whitelist IP(s) Used for Zoho Mail Webmail

Hello,

We have a small branch office, with around 6 users, who need to access their Zoho emails, via Webmail.. The site has a small-business router, capable of basic IP and port based Access Control, and regular net usage is restricted.  

What IP(s) and ports do we white-list, so that the users can access their Zoho webmail.