Hello twisted1919, when I check every other software or ESP email header they only embed one header in email. but for MW we got around 8 headers, Like bellow X-Mw-Tracking-Did: 4 X-Mw-Subscriber-Uid: bj216280m9164 X-Mw-Mailer: SwiftMailer - 5.4.x X-Mw-EBS: http://tracking.domain.com/lists/block-address X-Mw-Delivery-Sid: 12 X-Mw-Customer-Uid: qd822jpta8a47 X-Mw-Customer-Gid: 1 X-Mw-Campaign-Uid: ho58081qsl061As you are doing lot with MW now a days why can't you make MW header 1 or less as much you can. I know MW use these headers to read bounces, clicks and other operations on email especially bounces. like you can make one header for above as X-Mw-H: X-Mw-Tracking-Did-X-Mw-Subscriber-Uid-X-Mw-Mailer-X-Mw-EBS-X-Mw-Delivery-Sid-X-Mw-Customer-Uid-X-Mw-Customer-Gid-X-Mw-Campaign-Uid:with PHP you can get part of header you want to perform task. This will look email more clean, this is just an idea.