737 Captain reported the flight crew failed to send the Dangerous Goods (DG) acknowledgement message prior to aircraft movement under it's owe power.

Narrative

I forgot to acknowledge the final dangerous goods summary by sending the dangerous goods acknowledgment code message over ACARS before releasing the brake and pushing back. As we were disconnecting from the tug I asked the FO to check the ACARS message that had popped up and it was the reminder to send the acknowledgment. So I did at least send it before taxiing and taking off; but not before pushing.