mailq(1) on Linux
The text 03d04f3e7c7a, as Debian 13 (Trixie) shipped it.
Postfix to Sendmail compatibility interface
Flags it lists
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-Ac -
-Am -
-B -
-C -
-F -
-G -
-I -
-R -
-U -
-V -
-bH -
-bd -
-bh -
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-bl -
-bm -
-bp -
-bs -
-bv -
-f -
-i -
-m -
-n -
-o7 -
-o8 -
-oA -
-oi -
-om -
-q -
-qI -
-qR -
-qS -
-r -
-t -
-v