You need to configure the MFA settings for users who connect from the Boston office.

SC-300 emphasizes using Conditional Access with named locations to scope MFA—especially to exclude trusted corporate egress IPs. The materials state that administrators can define named locations by public IP ranges and “mark them as trusted” for policy exceptions. This aligns with the requirement: enforce MFA for all users, but exempt users authenticating from the Boston office. Because Azure AD evaluates the client’s public egress address, private RFC1918 ranges are never seen by Azure AD on the internet, so defining private IP ranges would not work. Likewise, the legacy “Trusted IPs” setting belongs to the old per-user MFA service settings; SC-300 guidance prefers Conditional Access named locations for modern MFA deployments and for combining with other conditions (apps, platforms, user risk, locations). Implementing the Boston office as a named location using its public egress IP range(s), and marking it trusted, lets you exclude that location from the tenant-wide MFA policy while still meeting the broader requirement to enforce MFA for everyone else and for on-prem apps published via Azure AD Application Proxy. In short: define Boston’s public IP as a named location and use it in your Conditional Access policy exclusion to satisfy the exemption precisely and securely.