Inboxes for Claude

Account-based outreach with Claude looks nothing like a sequence. There is no template with a first-name token; there is an agent that reads what a company has published, what the person has said, what changed last quarter, writes one email that could only have been sent to them, and sends it from a mailbox you connected. Claude connects to Google Workspace and Microsoft 365 accounts to read, draft, schedule and send, and our mailboxes are exactly those accounts, with you as admin.

So the sequencer is gone and the infrastructure question is not. A researched email leaving a mailbox with no reputation lands where a template does. The agent still needs mailboxes on domains built for cold email, authenticated, with sender history, and held to a daily pace. What changes is who holds the throttle: in a sequencer the cap is a setting, and when Claude sends it is an instruction and a schedule. This page is about connecting the mailboxes and keeping that instruction easy to keep. We sell the mailboxes, not Claude, and this is not a review of it.

The free API and MCP page lists every read-only tool, and the developers page walks through the keyed server the way a deployment platform documents a deploy: you create the account, the account issues the key, then the assistant connects. Preview before place.

• Separate domains, not the company one. It is tempting to connect Claude to the account you already have. That account is on the domain your invoices use, and cold outreach is filed against the domain. Our prewarmed orders come with the domain included, forwarded to your site, authenticated.
• Allow the connection as admin. You are the admin of every mailbox we deliver, which is what makes this possible: Google Workspace and Microsoft 365 both let an admin control which outside apps an account may authorise. If the connection is refused, that setting is where to look, in the Workspace admin console or the Microsoft tenant.
• Authentication already published. SPF, DKIM, DMARC and forwarding are configured before handover. Have Claude confirm it with the authentication checker, which it can call over the free MCP server.
• The list verified before the first send. Claude can research a person whose address no longer exists, and bounces are the signal that burns a new mailbox fastest. The waterfall calculator finds the cheapest verifier order for a list.
• A suppression list in the instructions. Replies, unsubscribes, customers, open deals. The suppression checker is the manual version; Claude needs the same check in its standing instructions before every send.

Written as what you are doing rather than as a click path, because Claude’s connection settings move and a page full of yesterday’s button labels makes everything around it look stale.

1. 1Size and order the fleet first. Connect the free MCP server, no key needed, and run plan_from_list against the recipient list and a daily target: a costed fleet before anything is bought. Then order in the portal, or let Claude preview and place the order over the keyed server with a key you issued. Mailboxes arrive within 48 to 72 hours of payment.
2. 2Connect each mailbox through Claude’s Google Workspace or Microsoft 365 connection. Sign in as the mailbox, authorise the connection, repeat per mailbox. Azure tenants are Microsoft 365 mailboxes and connect the same way. The credentials come to you at delivery; keep them with you and never paste them into a prompt.
3. 3Give Claude the cap as a standing instruction. The figures below, per mailbox per day, and an instruction to spread sends across the working day rather than at nine o’clock. With several mailboxes connected, have it rotate across them so no mailbox carries more than its share.
4. 4Schedule the runs. A scheduled task that researches the next accounts, writes, sends within the cap, and stops. Daily is the natural cadence; the cap is per day.
5. 5Read before you send. Each run checks the connected mailboxes for replies, out-of-office and unsubscribes first, and suppresses before it writes. The connection that sends can read; make sure the instruction says to.
6. 6Display name and signature, one pass across the fleet. A first cold email with no display name and a bare signature is advertising exactly that. One line of signature, no links in it.

An agent makes the fleet, not the cap, the variable. If the loop produces more emails than the connected mailboxes can send at these paces, the emails wait or the fleet grows; the calculator gives the number, and Claude can order it over the keyed server. Raising the per-mailbox figure instead is how a week of good research ends up in spam.

Prewarmed inboxes arrive with sender history; fresh inboxes are warmed by us for 14 to 21 days before handover. Our warmup then keeps running at 30 emails per inbox per day underneath Claude’s sending for as long as you hold the inboxes. There is nothing in the agent to switch off, and nothing to add.

One mailbox’s replies falling while the rest hold, bounces climbing on one domain: have Claude take that mailbox out of rotation, run the blacklist checker and the bounce analyzer on its bounces to tell the list from the domain, and message us on WhatsApp at +1 904 736 2539. Replacement inboxes are part of the package when deliverability drops, and keeping a few spare mailboxes connected is what makes a flagged one an inconvenience rather than a stopped agent.

Prewarmed inboxes include a free prewarmed .COM or .CO domain and send from the day they land: $8.00 per inbox per month on Google and Microsoft, $7.00 on a two-month commit, $6.00 quarterly. Azure is billed per tenant, $69 monthly, $60 on two months, $50 quarterly, with up to 100 inboxes on one domain, which at capacity is $0.69, $0.60 and $0.50 per inbox. Fresh inboxes on your own branded domains, warmed for 14 to 21 days first, run $3.50 to $2.00 per inbox per month on Google, $3.00 to $2.00 on Microsoft 365, and $50 flat for an Azure tenant. Every price is at /price.md, which an agent can read as plain text, and how it works covers everything between paying and the first send.

Can Claude send cold email from WarmInboxes mailboxes?

Yes. Every mailbox we deliver is an official Google Workspace, Microsoft 365 or Azure account with you as admin, and Claude connects to Google Workspace and Microsoft 365 accounts to read, draft, schedule and send mail. Connect the mailbox the way you would connect any Workspace or 365 account, and Claude sends from it. The sending goes through Google or Microsoft from the connected mailbox, not through anything of ours.

What does our MCP server add on top of the mailbox connection?

The free server at warminboxes.com/mcp needs no key and is read-only: every deliverability check, the infrastructure planner, and plan_from_list, which turns a recipient list and a daily target into a costed fleet. The keyed server at api.warminboxes.com/mcp works on your account: orders, build state, deliverability per domain, ordering more inboxes, and exporting into a sequencer for anyone who wants one. The key comes from the portal; you create the account yourself.

How many emails a day can Claude send per mailbox?

The same as a person or a sequencer: about fifteen a day on Google Workspace, eight on Microsoft 365, two on a full Azure tenant of 100. An agent does not change what a receiving server tolerates; it changes how fast you can exceed it. Give Claude the figure as a standing instruction, have it schedule sends across the day rather than in a burst, and size the fleet so the instruction is easy to keep.

Does one-to-one personalised email need warmed mailboxes at all?

Yes. Receivers judge the domain and the mailbox before they read a word, and a good email from a cold domain goes where a bad one does. Prewarmed mailboxes arrive with sender history; fresh ones are warmed for 14 to 21 days before handover, and our warmup keeps running underneath at 30 emails per inbox per day for as long as you hold them.

How does Claude handle replies and unsubscribes?

Through the same connection: it can read the mailbox it sends from. Instruct it to check for replies before each sending run, stop writing to anyone who has answered or asked out, and keep the suppression list it builds. An agent that sends and never reads is the fastest route to a complaint, and here the reading is one instruction away.

How fast do the mailboxes arrive?

Within 48 to 72 hours of payment, prewarmed and fresh alike, with SPF, DKIM, DMARC and forwarding configured before you log in. Prewarmed means no warmup wait once they land, not that they are delivered the same day.