Cleaner construct than a mailbox, in the usual case: what noreply actually needs is a valid deliverable address that discards replies without a mailbox's storage and license cost. Two good shapes by how graceful you want the discard:

The shared mailbox shape when you want replies auto answered: a shared mailbox noreply@ needs no license, receives replies so senders do not bounce and carries an auto reply, a rule or a mail flow response telling the human this address is unmonitored and where to actually write. Replies land somewhere reviewable if you ever care, and the auto response is the graceful touch bare setups miss.

The mail flow rule shape when you want silent clean rejection: no mailbox at all, instead a transport rule matching messages to noreply@ and rejecting them with a clear NDR, This address does not accept mail, please contact support@. Senders get an immediate honest bounce rather than silence, cheaper than any mailbox and appropriate when nobody should ever read a reply. The address still needs to exist as a valid recipient for your own outbound to pass authentication checks, satisfied by a mail contact or a distribution point the rule then intercepts.

The choice tracks intent: shared mailbox with auto reply when a stray important reply deserves a soft landing and a pointer, transport rule rejection when the address is purely one directional and silence should become a clear bounce. Either beats the current bounce or vanish, and both keep noreply properly deliverable so your application mail authenticates cleanly, the piece a nonexistent address quietly breaks.