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How to Add Multiple Mailboxes in FirstSales

Add several mailboxes and let campaigns rotate sends across them at modest daily limits so volume scales without torching sender reputation.

Tutorials
Mailboxes
min read
7 min
steps
6 · Intermediate

  1. Why send from many mailboxes

    Cold outreach at volume works best spread across several mailboxes, so no single inbox sends too much and burns its reputation. FirstSales includes unlimited mailboxes on every plan (Starter, Growth, Pro, and Business alike) so you're never capped on how many connectors you add. Plans meter monthly credits, not mailbox count.

    Why send from many mailboxes

  2. Add mailboxes one at a time

    The simple path: on the Connectors page, click Add Connector and connect each mailbox (Google, Microsoft, or SMTP/IMAP), repeating as many times as you need. The page shows a running count and a grid/list view of everything connected.

    See the "connect a mailbox" tutorial for the details of each connection type.

  3. Bulk-add mailboxes by CSV

    Adding a lot of SMTP/IMAP mailboxes at once? In the SMTP/IMAP flow, switch to the Bulk Upload (CSV) tab. Download the template, fill one row per mailbox, and upload.

    The CSV supports the full per-mailbox config, including email, IMAP/SMTP host, port, username, password, plus dailyLimit, warmupEnabled, warmupLimit, and warmupIncrement. The importer previews rows, lets you map columns, and reports how many succeeded or failed.

  4. Set each mailbox's daily send limit

    Open a connector and find its sending config. Daily Limit caps how many emails that mailbox sends per day (default 50, adjustable from 20 to 500. Keep individual mailboxes modest (real people don't blast hundreds of cold emails a day); scale total volume by adding more mailboxes, not by maxing one.

    • Send ceiling) an optional hard cap the auto-adjuster will never exceed ("Leave blank for no cap").

  5. Let auto-adjust protect reputation

    Leave Auto-adjust on (the default). It "manages this nightly based on yesterday's sending health": dialing a mailbox's volume down when metrics slip and back up as it recovers, without you babysitting it.

    The Sending health score bar shows each mailbox's standing, "scored nightly based on yesterday's sending metrics." A healthy fleet of many modest mailboxes beats a few pushed to their limit.

    Let auto-adjust protect reputation

  6. Warm up every new mailbox

    Each mailbox you add starts with no reputation. Enable warm-up on every one (or set warmupEnabled in the CSV) so they build sender reputation before you route real campaigns through them.

    Campaigns automatically send across your connected, healthy mailboxes: your job is to keep the pool warmed and within sane daily limits.

Pro tips

  • Scale by count, not by cranking one mailbox

    Unlimited mailboxes means the right move is more mailboxes at modest daily limits, not one mailbox at 500/day. Spread volume to protect every inbox's reputation.

  • CSV bulk import for fleets

    Adding many SMTP/IMAP mailboxes? Use the Bulk Upload (CSV) tab: one row per mailbox, with daily limit and warm-up settings baked in, instead of clicking through each.

  • Leave auto-adjust on

    Auto-adjust re-tunes each mailbox's daily volume nightly from yesterday's sending health. It's the cheapest insurance against a mailbox quietly torching its reputation.

  • Set a send ceiling if you're cautious

    The optional Send ceiling caps what auto-adjust can ever reach. Blank means no cap; set a number when you want a firm upper bound per mailbox.

Frequently asked questions

How many mailboxes can I add?

Unlimited: it's a feature on every plan tier (Starter, Growth, Pro, Business). There's no per-plan mailbox cap; plans differ on monthly credits, not mailbox count.

Can I add many mailboxes at once?

Yes. In the SMTP/IMAP flow use the Bulk Upload (CSV) tab: download the template, one row per mailbox, and upload. It previews rows, maps columns, and reports successes and failures.

What's the daily send limit per mailbox?

Daily Limit defaults to 50 and can be set from 20 to 500 per mailbox. For cold outreach, keep it modest and add more mailboxes to grow total volume.

What does Auto-adjust do?

It manages a mailbox's daily volume automatically each night based on yesterday's sending health: lowering it when metrics dip and raising it as the mailbox recovers. It's on by default.

What is the Send ceiling?

An optional hard cap that auto-adjust will never exceed. Leave it blank for no cap, or set a number to bound how high a mailbox's daily volume can climb.

How is total sending volume shared across mailboxes?

Campaigns send across your connected, healthy mailboxes automatically. You control the total by how many mailboxes you connect and each one's Daily Limit: more warmed mailboxes at modest limits is the safe way to scale.

Do I need to warm up each new mailbox?

Yes. Every new mailbox starts with no reputation, so enable warm-up on each (or set warmupEnabled in the CSV) before routing real campaigns through it.

What is the Sending health score?

A per-mailbox score, scored nightly based on yesterday's sending metrics, shown as a bar in the sending config. It's what auto-adjust reads to decide whether to raise or lower that mailbox's volume.

Mailboxes

Outreach that keeps going after you log off.Leads, emails, follow-ups and replies, handled.

Connect unlimited mailboxes and let AI agents find leads, write each email and follow up. Or send your own templates in manual mode. From $29/mo.

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Install with AI

Your coding agent sets up the FirstSales CLI and skills for you.

Prompt for Claude Code

I'm setting up FirstSales (https://firstsales.io), an AI outbound sales platform: campaigns, contacts, a reply inbox, deliverability and lead signals. Help me get my workspace sending real, good emails end to end, from Claude Code.

Read these first so you know how FirstSales works:
- Developer docs and API: https://developer.firstsales.io
- CLI: https://www.npmjs.com/package/@firstsales.io/cli
- Skills for coding agents: https://github.com/firstsalesio/firstsales-skills (read README.md and GUIDE.md)

Setup
1. Install the CLI: npm install -g @firstsales.io/cli
2. Install the FirstSales skills:
   claude plugin marketplace add firstsalesio/firstsales-skills
   claude plugin install firstsales@firstsales
3. Ask me if I already have a FirstSales account. If not, send me to https://app.firstsales.io to sign up.
4. Ask me to create an API key under Settings → API → API Keys, with only the scopes we need.
   Never ask me to paste the key into this chat. Tell me to run this in my own terminal, so the key stays hidden:
   read -rs FS_KEY && firstsales auth login --api-key "$FS_KEY"; unset FS_KEY
5. Run `firstsales whoami` and tell me which workspace and organisation we are connected to.

Then ask me about my business: what I sell, who I sell to (roles, company size, countries), my best customers, and what I use today for outbound (tools, lists, mailboxes). Walk me through:
1. Teaching FirstSales my business: website, offer, proof points and case studies in the knowledge base, so the AI writes like someone who knows the product.
2. Connecting my sending mailboxes and checking my sending domain: SPF, DKIM, DMARC and warm-up. If anything is unhealthy, tell me the exact DNS record to add.
3. Bringing in contacts: import my CSV or CRM export into a clean list, remove duplicates and bad emails, and block domains I must never email (customers, competitors, my own).
4. Building my first campaign: the right list, senders, steps and timing. Write the sequence with me, show me the drafts, and do not launch until I say yes.
5. Setting up Signals if it fits: find people engaging with LinkedIn posts about topics my buyers care about, and turn them into leads.
6. Inviting my team and giving each person the right access.

Once campaigns run, show me how to work the reply inbox from here: which replies need an answer, draft responses in my voice, and move good conversations into deals. If I use Cal.com, connect it so follow-ups can offer my booking link (not the first email).

Throughout, as you learn about my business, proactively suggest and help create:
- Reply templates for the questions and objections my prospects are likely to raise, based on my product, site and codebase if you can see them.
- Campaign ideas and segments worth testing, with the reason for each.

Safety rules:
- Show every change as a dry run (--dry-run) first and wait for my yes. Never send emails, launch campaigns or delete anything without my yes.
- Tell me before anything that spends credits, and how many.

Be opinionated. If the docs give a sensible default, just use it. Don't make me choose between five options.
Developer docs ↗npm: @firstsales.io/cli ↗GitHub: firstsales-skills ↗