Outreach
Reply rate
Reply rate is the share of contacted businesses that answer, positively or not. For cold B2B outreach to a well-targeted list, somewhere between 2% and 8% is a realistic range.
It is the only cold-outreach metric worth optimising, because it is the one the measurement cannot fake. Open rates depend on a tracking pixel that a growing share of mail clients load automatically or block entirely, which makes the number roughly meaningless in either direction.
Count negative replies too. A campaign generating 6% replies of which most are refusals is a targeting problem you can see and fix; a campaign generating 0.3% replies gives you nothing to learn from at all.