This suggests a low "bounce" or "failure" rate. HQ lists usually mean the data hasn't been "public" for long and isn't yet saturated or flagged by security systems.
This indicates that the credentials aren't just for a random website; they are for email accounts (IMAP/POP3/Webmail). This is high-value because a compromised email is a "master key" to reset passwords for every other service the user owns (Amazon, Netflix, Banking, etc.). 220k mail access valid hq combolist mixzip hot
Decoding the Jargon: What is a "220k Mail Access HQ Combolist"? This suggests a low "bounce" or "failure" rate