Merge branch '364683-update-service-desk-accepted-headers-doc' into 'master'

Resolve "Service Desk seems to ignore "Accepted Headers""

See merge request gitlab-org/gitlab!92807

doc/administration/incoming_email.md

@@ -75,11 +75,12 @@ Email is processed correctly when a configured email address is present in one o
 (sorted in the order they are checked):
 
 - `To`
-- `References`
 - `Delivered-To`
 - `Envelope-To` or `X-Envelope-To`
 - `Received`
 
+The `References` header is also accepted, however it is used specifically to relate email responses to existing discussion threads. It is not used for creating issues by email.
+
 In GitLab 14.6 and later, [Service Desk](../user/project/service_desk.md)
 also checks accepted headers.