bounce message

n. [common] Notification message returned to sender by a site unable to
relay email to the intended Internet address recipient or the next link in a
bang path (see bounce , sense 1). Reasons might include a nonexistent or
misspelled username or a down relay site. Bounce messages can themselves
fail, with occasionally ugly results; see sorcerer's apprentice mode and
software laser. The terms bounce mail and barfmail are also common.