The -d27.5 debugging switch tells sendmail to print several addresses with printaddr( ) (Section 16.3) as each one is handled.

When an address is aliased to another, the original needs to be marked as one that shouldn't be delivered. The QS_DONTSEND here means just that:

alias: QS_DONTSEND output of printaddr( ) here (Section 16.3)

If there was a self-reference, the retained address is printed like this:

sendtolist: QS_SELFREF output of printaddr( ) here (Section 16.3)

If the original (before the test for a self-reference) is not the same as the retained address, the original must be marked for nondelivery:

sendtolist: QS_DONTSEND output of printaddr( ) here (Section 16.3)

If an address resulted from a :include: or ~/.forward file, it will have a controlling user associated with it. That controlling user's address needs to be marked for nondelivery:

include: QS_DONTSEND output of printaddr( ) here (Section 16.3)