Claude skill
List Segmentation
Who hosts the people on this list?
Cold email lands better when the sending platform matches the recipient’s. Point this at a CSV and it works out who actually hosts every address on it, so the campaign can be sent from the right place instead of one pile of mailboxes aimed at everyone.
What it runs
- MX lookup per domain — Who really hosts the mailbox, which is not always who the brand suggests
- Gateway detection — Proofpoint, Mimecast, Barracuda and friends, which filter before the mailbox sees anything
- Deduplication — A 10,000-row list is usually a few hundred unique domains
- Order sizing — Mailboxes and domains needed per segment, from the infrastructure planner
What you get back
- The split as counts and percentages, with the MX evidence behind each call
- Which platform to send each segment from, and why
- Gateway-protected rows flagged separately, because mixing them in makes every other segment look worse than it is
- A mailbox count per segment
Install it
One file, from GitHub. It calls the free WarmInboxes API, so there is no key and nothing to sign up for.
mkdir -p ~/.claude/skills/list-segmentation curl -sL https://raw.githubusercontent.com/Huz-ai-fa/warminboxes-claude-skills/main/list-segmentation/SKILL.md -o ~/.claude/skills/list-segmentation/SKILL.md
Then just ask
You do not name the skill. Its description tells Claude when it applies.
- “Split this lead list by email provider”
- “Are my prospects on Google or Microsoft?”
- “How many of these companies sit behind a spam gateway?”
Every answer cites the check behind it, so anything Claude tells you can be re-run by hand. A clean result is reported clean, with nothing to buy.