# Email hosting by company size, age, industry and list

Which company runs a domain's inbound email, read from DNS, for the Inc 5000
(2026), Y Combinator companies, the Fortune 500 and unicorns. Built for the
Installmap post "Microsoft passes Google at about 50 employees in the Inc 5000".

## Files

- `by_group.csv`: one row per company list.
- `inc5000_by_employees.csv`: Inc 5000 by the employee band the list publishes.
- `inc5000_by_founded.csv`: Inc 5000 by founding year.
- `inc5000_by_founded_and_employees.csv`: Inc 5000 by founding year group and
  employee band together.
- `inc5000_by_industry.csv`: Inc 5000 industries with 60 or more companies.
- `yc_by_batch_year.csv`: Y Combinator by batch year block, all companies and
  companies YC lists as active.
- `fortune500_on_google_workspace.csv`: the 20 Fortune 500 companies whose MX
  host is Google, with rank and domain.

## Columns

- `segment`: the list, band, industry or year block.
- `domains`: companies counted in that segment.
- `google_workspace`, `microsoft_365`: companies on that host, and the
  `_pct` columns as a percentage of `domains`.
- `behind_gateway`: companies whose MX host is an email filtering service
  (Proofpoint, Barracuda, Mimecast, AppRiver, Sophos, Cloudflare Email
  Security, Hornetsecurity, Trend Micro, SpamTitan).
- `proofpoint`: companies whose MX host is Proofpoint.
- `active_domains`, `active_google_workspace_pct`, `active_microsoft_365_pct`
  (YC file only): the same shares for companies YC lists as active.

License: CC BY 4.0. Source: Installmap, October 2026.