As a result of a policy by some Internet Service Providers (ISPs), e.g. Comcast and Verizon, mail you send from Office 365 Outlook while using these external ISPs may receive very high spam scores. This may result in recipients finding the mail was delivered to their Junk Mail/Spam folders or blocked entirely. This applies to mail sent using your desktop email client, Outlook Web App (OWA), or mobile device connected to wireless on the affected ISP.
Some have been intentionally adding their own networks to multiple spam blacklists in an effort to control how mail flows out of their network. It is the policy of these ISPs that mail should be directed through their own outgoing mail servers rather than external mail services such as Office 365. For example, here is a description of Verizon’s policy.
As a best practice, it is recommended that you always use BU’s VPN when connecting to BU resources or Office 365 when off campus. In addition to providing additional security features, using the VPN will assign you a BU network address for the duration of your VPN session, which should allow you to bypass these blacklisting policies on your external network service provider. If use of the VPN is not feasible, you could use the outgoing mail server provided by your external network service provider, or change your service to a different provider that isn’t blacklisting its own network.