Bulk email, sometimes referred to as grey mail, or gray mail, is a type of email that is difficult to classify for all users at a global level. Bulk or gray email is email that some users want but others consider spam. For example, some users want their email from Amazon Local’s Daily Deals or invitations to an upcoming conference on cyber security. Other users consider this email spam.
The reason that it is called gray mail is because it is not a spam/non-spam decision, it is a shade of gray:
In other words, there is no solution that will satisfy all users.
To get around this problem, Office 365 has an option that allows tenant administrators to mark all messages that the service identifies as bulk as spam (see Advanced Spam Filtering Options). If an administrator selects this option, and users start seeing messages that they want in their junk mail folders, they can add bulk email that they want to their safe senders list. Alternatively, administrators can create Exchange Transport Rules (in Exchange Online) or Policy Rules (in FOPE) to allow certain types of messages at a global level for everyone.
To determine how Office 365 decides that sending IP addresses as Bulk emailers, we use the following criteria:
The above summary should provide all the information necessary to understand Bulk Email identification in Office 365.
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