Each recipient address for a mail message is added one-by-one to an
internal list of recipients. The -d25.1 (a.k.a.
-d25) debugging switch causes
sendmail to print each address as it is added to
ctladdr= output of printaddr( ) here (Section 16.3)
After each is added, those that have selected a delivery agent with
the F=A (F=A) and
F=w (F=w) flags set are
further processed by aliasing and by reading the
user's ~/.forward file. Each
new address that results from this processing is added to the
list, and any duplicates are discarded.