Bulk complaint level
A 0 to 9 rating Microsoft 365 gives mail from bulk senders, higher when the sender draws more complaints. Mail at or above the threshold goes to junk by default.
What it means
Microsoft 365 assigns a BCL to inbound messages from bulk senders and adds it to the message in an X-header. Microsoft uses internal and external sources to identify bulk mail. A BCL of 0 means the message is not from a bulk sender; 1 to 3, a bulk sender that generates few complaints; 4 to 7, a mixed number of complaints; 8 and 9, a high number.
The default threshold is 7 in the default anti-spam policy, 6 in the Standard preset and 5 in the Strict preset. Mail at or above it is treated as bulk: delivered to the Junk Email folder by default, or quarantined under the Strict preset.
Microsoft calls such mail bulk mail or gray mail. Since administrators can lower the threshold, a sender with a mid-range BCL can reach the inbox at one company and junk at another.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- Microsoft Learn: Bulk complaint level (BCL)learn.microsoft.com
- Microsoft Learn: Anti-spam protectionlearn.microsoft.com
All 432 terms in the glossaryThe wiki: blocklists and bounce codes