Infraforge and Lumbox both get filed under "email infrastructure," and both appear in lists of alternatives to agent email products, but they sit on opposite sides of the mailbox. Infraforge is built for sending cold email at volume without landing in spam. Lumbox is built so an AI agent can have an address, receive mail at it, and act on what arrives. The Infraforge details below come from its homepage and FAQ as of September 2026.
What Infraforge sells
Infraforge describes itself as private cold email infrastructure with dedicated IPs. You buy domains and mailboxes through it, and it sets up DMARC, SPF, DKIM and a custom tracking domain for each domain automatically, with bulk DNS updates across all of them. It offers prewarmed domains and mailboxes for teams that want to start sending immediately, SSL and domain masking so a domain can show a branded site, extra IPs, workspaces per project, and a combined view of every mailbox's mail called Masterbox.
It does not include the sequencer. Infraforge is the layer underneath: its site says it works with Salesforge and any other sending software, and it exposes an API, an MCP server and a CLI. Pricing is per mailbox, from $4 down to $3 a month, and the FAQ says there is no free trial because the product only makes sense once you have bought domains and mailboxes. The same site points teams that want Google or Microsoft mailboxes to a separate product, Primeforge.
What Lumbox sells
Lumbox gives each agent or task its own inbox through one API call, parses every inbound message for verification codes, links and a category, and offers endpoints that block until a matching email arrives. Agents can send, reply and forward from the same address. Plans are priced by inbox count and monthly volume: 3 inboxes free, then $9, $29 and $99 a month.
On the sending side Lumbox is deliberately plain. Addresses on the shared trylumbox.com domain send through Amazon SES. Inboxes on your own verified domain send through whatever provider you register as your default (SMTP, SES, SendGrid, Postmark, Resend, Mandrill or Klaviyo), or the platform default if you register none. There is no warm-up, no IP management, no domain masking and no mailbox rotation. There are limits instead: 3 sends a minute on free up to 120 on Scale, monthly caps from 100 to 50,000 emails, a slower ramp for brand-new free accounts, a suppression list for bounces and complaints, and checks that stop shared-domain inboxes from impersonating other brands.
The question that decides it
Look at which direction the important mail travels.
Cold outreach is outbound first. Thousands of messages go to people who did not ask for them, and the product that matters is whatever keeps those messages out of spam folders: separate domains, dedicated IPs, warm-up, rotation and monitoring. Infraforge is built for that problem and Lumbox is not. Lumbox's highest plan caps sending at 50,000 emails a month and runs on shared provider infrastructure unless you bring your own.
Agent signups and verifications are inbound first. The agent submits an address to a form and waits for one email, then reads a code or clicks a link. Deliverability barely enters into it, because the sender is the service the agent signed up for. What matters is getting a fresh address instantly, receiving the email within seconds, and reading the code without writing a parser. That part is what Lumbox handles.
Side by side
| Infraforge | Lumbox | |
|---|---|---|
| Main job | Infrastructure for sending cold email | Inboxes for AI agents |
| Pricing unit | Per mailbox, $4 to $3 a month | Per plan: 3 inboxes free, then $9, $29, $99 |
| IPs | Dedicated IPs, extra IPs available | Shared provider IPs, or your own provider |
| DNS setup | Automated DMARC, SPF, DKIM, tracking domain | API returns records to add; automatic setup on Cloudflare DNS |
| Warm-up | Prewarmed domains and mailboxes | None |
| Inbound side | Masterbox view across mailboxes | Codes and links parsed on arrival, long-poll wait endpoints |
| Integrations | API, MCP, CLI, sending tools like Salesforge | REST API, TypeScript and Python SDKs, MCP server |
| Trial | None; you buy domains and mailboxes | Free plan, no card |
Controlling deliverability on the Lumbox side
If an agent sends real correspondence from your own domain (order follow-ups, vendor questions, replies to people who wrote in), you can route that mail through a provider you already trust and preview each message before it goes. Two calls cover it:
# 1. Make your own provider the default for custom-domain sends
curl -X POST https://api.lumbox.co/v1/smtp-configs \
-H "X-API-Key: $LUMBOX_API_KEY" -H "Content-Type: application/json" \
-d '{"provider":"POSTMARK","api_key":"...","from_name":"Ops Agent","is_default":true}'
# 2. Validate a send without sending it
curl -X POST https://api.lumbox.co/v1/inboxes/inb_.../send \
-H "X-API-Key: $LUMBOX_API_KEY" -H "Content-Type: application/json" \
-d '{"to":"orders@vendor.example","subject":"PO 1182 status","text":"...","dry_run":true}'
# {"dry_run":true,"would_send":{"from":"agent@ops.example.com","to":["orders@vendor.example"],
# "cc":[],"subject":"PO 1182 status","body_preview":"...","body_chars":212,
# "has_html":false,"message_id":"<msg_...@ops.example.com>"}}The default provider only applies to inboxes on your own domain. Inboxes on trylumbox.com always send through Lumbox's SES account, so their reputation is shared with every other Lumbox customer on that domain. That is fine for replies and low-volume correspondence and wrong for anything resembling a campaign.
When you need both
An outbound sales agent is the case where both show up. The sequences go out through Infraforge mailboxes and a sequencer, and replies come back to those mailboxes. The same agent also needs to sign up for data tools, confirm webinar registrations, or receive login codes for the services it uses, and those belong on separate Lumbox addresses. Keeping the two sets of domains apart means a cold-outreach domain that picks up spam complaints does not take the agent's own logins down with it.
For the sending side in more depth, shared versus dedicated sending domains and warming up a new domain cover the basics, and the bring-your-own-SMTP post walks through provider configs in Lumbox.