The RETRY command is used to retry delivering mail sent BY or TO you.
You need
never use the RETRY command, but if your mail TO or FROM anyone is queued for
any reason and you are impatient, you can use this command to run MAIL,
which will search for queued mail sent by your login programmer name
and, upon finding some, make another attempt to send it immediately.
For instance, you were editing your mail file at the time the
message was sent.

PLEASE DO NOT TYPE ↑C AFTER GIVING THIS COMMAND, OR YOU MAY LOSE A QUEUED
MESSAGE.  To abort RETRY early, type ESC I (↑← I on non-displays).  If you
only want to retry delivering mail TO you (e.g., that was queued because
you were editing your message file), type RETRY/INPUT (RETRY/I is enough);
this is the most common thing you'll want RETRY for.  To retry only
outgoing mail (from you), type RETRY/OUTPUT (RETRY/O); this often takes a
while if you have mail going out onto the ArpaNet.

The remind phantom itself will automatically try about once every 3 hours
to send outgoing queued ArpaNet mail; it retries about every 10 minutes to
deliver queued mail at SAIL.  If it finally gives up (after three days'
failures) it will both MAIL and SEND you a message telling of the failure
of the mail attempt.  An outcome of "expired" means the mailing failed for
three days.

For more information, see the MAIL section and the MAIL appendix in the
Monitor Command Manual, SAILON-54.6, online as MONCOM.BH[S,DOC].