Mailbox rhymes with:
boombox, breadbox, fischbach's, gearbox, icebox, jukebox, matchbox, saltbox, sandbox, skybox, soapbox, tarbox, tinderbox
Mailbox sounds like:
mailbag, mailbags, mailboxes, malpass, malveaux, minilabs, molpus, molpus', molpus's, muehlebach