Get a VPS
A mail server has two requirements most app hosts don’t: TCP port 25 must be open (that’s how mail arrives), and you need a domain you control. The good news: the workload is tiny — 1 vCPU / 1 GB RAM is plenty — so the cheapest tier of any of these works.
One thing that trips people up: when providers “block port 25”, they almost always mean outbound (anti-spam). Receiving mail works out of the box nearly everywhere — and receiving is the core of what your agents do (OTP codes, verification links). For sending, you either ask the provider to open it or route outbound through a relay like Amazon SES — the deliverability guide covers both.
Recommended
Section titled “Recommended”| Provider | From | Why this one | Port 25 |
|---|---|---|---|
| RackNerd (ad) | ~$11/year | The rock-bottom option and our top pick: open both ways, clean IP pool, rDNS via ticket. Takes Alipay, PayPal, cards, crypto. Watch their flash deals | Open both ways |
| Contabo | $4.50/mo | Most horsepower per dollar (4 vCPU / 8 GB). Official CLI + API. Card/PayPal only | Open both ways (new accounts throttled ~25 msgs/min) |
| GreenCloud (ad) | ~$15/year | Proven by us: our own mail server runs on it. Budget KVM flash deals from $15/year — they sell out fast, grab one when in stock. Takes Alipay, WeChat, cards | Open both ways |
| Evoxt (ad) | $2.99/mo | Cheapest monthly plan. Takes Alipay, PayPal, cards, BTC/USDT | Inbound open; outbound via support ticket |
| UpCloud | $3.50/mo | Excellent automation: REST API, upctl CLI, Terraform. Card/PayPal only |
Inbound open; outbound via support ticket |
| Vultr (ad) | $3.50/mo | Best automation (official CLI, API, and an official MCP server) and easy sign-up — but since 2026 they rarely approve outbound port 25 for self-hosted mail. Pick Vultr only if you plan to send via a relay (SES) anyway | Inbound open; outbound effectively closed |
Which one should I pick?
- Tightest budget → RackNerd (~$11 for a whole year) or Evoxt ($2.99 monthly, no yearly commitment).
- Paying with Alipay or WeChat → RackNerd, GreenCloud, or Evoxt. (Contabo, UpCloud and Vultr take cards/PayPal; Vultr also takes Alipay.)
- Most machine per dollar → Contabo’s 4 vCPU / 8 GB is overkill in the good way.
- Agent-driven setup → UpCloud and Vultr have the cleanest APIs if you want your agent to provision the box itself.
Avoid for mail
Section titled “Avoid for mail”- DigitalOcean — officially discourages self-hosted mail and often refuses to open outbound 25.
- Hetzner (new accounts) — outbound 25 stays closed for about a month.
- Google Cloud / Azure — port 25 hard-blocked, no exceptions.
- Oracle Cloud free tier — outbound 25 effectively blocked, and idle VMs get reclaimed (a quiet mail server looks idle).
And a domain
Section titled “And a domain”Already own any domain? You don’t need to buy a new one. A subdomain works
fine — point agents.yourdomain.com at the mail server and your agent
addresses look like fox-k7d2@agents.yourdomain.com. Your main site’s email
is untouched. Skip straight to the quickstart.
Buying a new domain? Any registrar works — you’ll create MX/SPF/DKIM records by hand once, and our dns-records.sh prints exactly what to paste. These are the picks we recommend:
| Registrar | .com first year | Renews at | Why this one |
|---|---|---|---|
| Spaceship | ~$9 (promos from ~$3) | ~$10 | Clean REST API with zero gating — register, contacts, DNS all API. Takes Alipay, PayPal, BTC |
| Porkbun | ~$11 | ~$11 | Official MCP server + full API, per-key spend caps (agent-safe), fair renewal pricing |
| NameSilo (ad) | ~$11 | ~$11 | Free API with no spending threshold, cheap TLD promos |
| Cloudflare | $10.46 (at-cost) | at-cost | No markup ever, and the best DNS API anywhere — but your domain must use Cloudflare nameservers |
| Namecheap | ~$10 | ~$14 | The biggest name, but the API requires $50 of spend history — not automation-friendly for new accounts |
A trick worth knowing: you can register at one place and host DNS at another. Buy the domain at Spaceship or Porkbun, then move DNS hosting to Cloudflare (free) to get its best-in-class DNS API for automation.
Which TLD? If the mailbox is mainly for receiving OTP codes and
verification links, a cheap TLD is fine — .xyz starts around $1/year and
.top renews at about $4/year, the cheapest long-term option. Deliverability
barely matters for receiving, because the sender is Gmail or GitHub, not you.
Two caveats: a few websites reject sign-ups from cheap-TLD addresses, and if
your agents will send mail to real people, spend the extra $10 on a .com —
cheap TLDs carry spam-reputation baggage with some mail filters.
Watch the renewal price, not the sticker price. A $1 first-year .xyz
typically renews at $11–20. Every price in the table above shows the renewal,
and Spaceship, Porkbun, and NameSilo are known for small first-year-to-renewal
gaps.
Avoid registrars that require real-name verification with manual review — that’s a human-in-the-loop step an agent can’t pass.
Links marked (ad) are affiliate links — same price for you, they support the project. They never change the ranking: picks are ordered by how well they run a mail server for agents, nothing else.