kumomta/docs/reference/message/remove_x_headers.md

message:remove_x_headers([NAMES])

When called with no parameters, removes all headers with an "X-" prefix from the message.

When called with a list of header names, only those headers, if present in the message, will be removed from the message.

For example, with a message content of:

X-Campaign-ID: 12345
X-Mailer: foobar
Subject: the subject

The body

calling:

message:remove_x_headers()

will result in the body changing to:

Subject: the subject

The body

but calling:

message:remove_x_headers { 'x-campaign-id' }

will result in the body changing to:

X-Mailer: foobar
Subject: the subject

The body