The RETRY command is used to retry sending your queued mail.  You
need never use the RETRY command, but if your mail to anyone is
queued for any reason and you are impatient, then 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.

PLEASE DO NOT TYPE ↑C AFTER GIVING THIS COMMAND, OR YOU MAY LOSE A
QUEUED MESSAGE.

The remind phantom itself will automatically try about once every 3
hours to send queued mail.  When it finally succeeds or else gives up
(after three days' failures), it will both MAIL and SEND you a
message telling the outcome of the mail attempt.  An outcome of
"expired" means the mailing failed for three days.

For more information, see the file MAIL.BH[UP,DOC].