Yeah, you could do it with Postfix. Essentially you want to put any messages to firstname.lastname@example.org into a quarantine for processing which would be essentially putting it into the HOLD queue in postfix for processing.
There is probably a better lookup table to use, but, you could test with header_checks postfix file. /etc/postfix/header_checks - You could make this check for TO: email@example.com and send to HOLD queue (note... there is probably faster/better lookup table for this)
If you read the comments in the header_checks file for HOLD it says...
# Arrange for the message to be placed on the hold
# queue, and inspect the next input line. The mes-
# sage remains on hold until someone either deletes
# it or releases it for delivery.
# Mail that is placed on hold can be examined with
# the postcat(1) command, and can be destroyed or
# released with the postsuper(1) command.
# Note: use "postsuper -r" to release mail that was
# kept on hold for a significant fraction of $maxi-
# mal_queue_lifetime or $bounce_queue_lifetime, or
Would mean logging in and manually checking the emails in the hold queue by command line, but, pretty much what you want?