Jagex Messages stay visible for three months and then disappear.
The messages were all sent out between 1st and 6th December 2022 meaning they dropped out of players 'Messages' tabs between 1st and 6th March 2023.
You had to save your passcode into an offsite file before it dropped out of existence.
What date was the email?
check your 'Messages' tab again as the message has been resent.
The JMod apologised that it won't be very pretty looking as he didn't bother with all the HTML that the original message had but it
will
contain the passcode.