When submitting your manuscript to an agent or a publisher, INCLUDE A STAMPED ENVELOPE WITH YOUR ADDRESS.
At the very least, you should always seek and welcome constructive criticism. If you don’t add an addressed envelope with sufficient pre-paid postage, you will not be contacted with positive news or constructive advice. Publishers will often take the time to explain (even if briefly) why they decided not to accept your manuscript.
Of course, for larger/international presses, a template rejection letter is more likely if you send your manuscript without an agent, but sending personalized letters is a tradition many publishing houses still hold.