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Sending infrastructure

Sending infrastructure that grows with your mailboxes, not your bill.

Connect as many Google, Microsoft and SMTP/IMAP mailboxes as you need, on every plan. Give each one a safe daily limit, let campaigns send across the ones you choose, and run tracking on your own domain. More volume means more mailboxes, never one inbox pushed too hard.

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The Connectors page in the FirstSales sample workspace, with several connected email mailboxes, a calendar and a notification bot, each showing when it was last verified
  • 01

    Unlimited mailboxes and workspaces on every plan

  • 02

    Google, Microsoft or any SMTP/IMAP provider

  • 03

    Bulk import up to 5,000 mailboxes from one CSV

  • 04

    From $29/mo, with no per-mailbox fees

The problem

More volume usually means more burned domains.

Scaling cold email is an infrastructure problem before it is a copy problem. Push too much through one mailbox and its reputation drops. Spread it by hand and the spreadsheet becomes the risk.

One mailbox hits a ceiling fast

A single inbox can only send so much before providers slow it down or start filtering it. Real people do not send hundreds of cold emails a day, and mail providers know it.

Per-mailbox pricing punishes growth

When every extra inbox costs extra, the safe move of adding mailboxes becomes the expensive one. Teams end up overloading the few they have.

Manual juggling breaks things

Tracking which inbox sends next, which one is cold and which one lost access is how a mailbox quietly takes a spike or a campaign quietly stops.

How it works

Connect, pool, send. Then add more.

Your sending setup lives on the Connectors page. Every campaign sends from connectors, so this is the first thing to set up and the place you come back to when you grow.

  1. 01

    Connect your mailboxes

    Click Add Connector and pick Google, Microsoft or SMTP/IMAP. Add one at a time, or bring a whole fleet in from a CSV. There is no cap on how many.

  2. 02

    Set safe limits and warm up

    Give each mailbox a modest daily limit, leave Auto-adjust on and turn on warm-up. New mailboxes build reputation before they carry real campaigns.

  3. 03

    Choose senders per campaign

    In each campaign, pick the mailboxes that should send. FirstSales spreads the sends across them. Need more volume later? Add more senders.

The volume math

Daily volume is mailboxes times a safe limit.

There is no secret dial for more sends. Each mailbox has a daily limit, and a campaign sends across the mailboxes you give it. To send more, add mailboxes. Keep each one modest.

StageMailboxesPer mailbox, per dayDaily volume
Getting started5× 40
200
Growing15× 40
600
At scale40× 40
1,600

Sample numbers to show the math, not a target. Daily Limit can be set from 20 to 500 per mailbox, with a default of 50. Auto-adjust tunes it each night from that mailbox's sending health.

What you get

A sending layer that scales by adding, not pushing.

Everything you need to run outreach across many mailboxes, without a spreadsheet and without paying more for every inbox.

  • Unlimited mailboxes

    Every plan includes unlimited mailboxes and unlimited workspaces. Plans meter monthly credits, not how many inboxes you connect.

  • Any provider

    Google Workspace and Microsoft connect with a sign-in and no stored password. Any other provider connects with SMTP and IMAP details.

  • Bulk import

    Bring in up to 5,000 SMTP/IMAP mailboxes from one CSV, with daily limits and warm-up settings set per row.

  • Per-mailbox limits

    Each mailbox gets its own daily limit, from 20 to 500. Auto-adjust tunes it each night from yesterday's sending health.

  • Your own tracking domain

    Open, click and unsubscribe tracking runs on a subdomain you own. You add one CNAME. SSL is set up for you.

  • Mailboxes that stay connected

    When a Google or Microsoft mailbox loses access, it shows an alert and a Reconnect Account button. Its settings stay in place.

From one inboxto a sending fleet

Four parts of your sending infrastructure, and what each one does for you.

  1. Connect

    Connect any mailbox, and know it works before you save

    Open Connectors, click Add Connector and choose Google, Microsoft or SMTP/IMAP. Google and Microsoft open a sign-in popup. SMTP/IMAP asks for your server details, then Test connection must pass before Add account unlocks, so a broken mailbox never slips into a campaign.

    • Sign-in for Google and Microsoft. A revocable token, never your password.
    • SMTP/IMAP for the rest. Sending and reading, so replies land in your FirstSales inbox.
    • Tested before saved. Wrong host, port or app password shows up right away.
  2. Bulk import

    Bring a whole fleet in from one CSV

    In the SMTP/IMAP flow, switch to Bulk Upload (CSV). Download the sample file, add one row per mailbox and upload it. Columns map by name, a preview flags any bad rows, and the import reports how many mailboxes succeeded and why any failed.

    • Up to 5,000 rows. One file under 5MB. Split bigger fleets and use Import More.
    • Settings per row. Daily Limit and the warm-up columns travel with each mailbox.
    • Checked before import. Email format, hosts, credentials and port ranges are validated first.
  3. Sender pool

    Pick the senders, and the sends spread across them

    In each campaign, open Email Accounts and choose the warmed, authenticated mailboxes that should send. The selector shows how many you picked. FirstSales spreads the campaign across them, each within its own daily limit. To grow, add senders in waves.

    • Choose senders per campaign. Different campaigns can use different mailboxes.
    • Each mailbox keeps its limit. No single inbox takes the whole campaign.
    • Grow by adding senders. More warmed mailboxes means more daily volume.
  4. Tracking domain

    Run tracking on a domain you own

    In workspace settings, open Tracking Domains and enter a subdomain such as track.yourcompany.com. Add the one CNAME it shows, and FirstSales handles the rest, from the CNAME check to SSL to HTTPS. The card re-checks every 5 minutes until it reads Verified.

    • One record. A single CNAME. No certificate to upload.
    • Clear status. Pending, CNAME OK, SSL OK, then Verified.
    • Your own links. Opens, clicks and unsubscribes tracked on your domain.
Three ways to connect

Pick the connection that fits each mailbox.

Every sending mailbox in FirstSales is a connector. Google and Microsoft connect with a sign-in. Anything else connects with server details. Here is how the three compare.

QuestionGoogleMicrosoftSMTP / IMAP
How you connectSign in with Google (OAuth)Sign in with Microsoft (OAuth)Server details for sending and reading
Is your password stored?No, a revocable tokenNo, a revocable tokenYes, use an app password if you can
Before you can saveApprove access in the popupApprove access in the popupTest connection must pass
If access lapsesReconnect Account, settings keptReconnect Account, settings keptRe-test, or re-add with new details
Many at onceOne sign-in per mailboxOne sign-in per mailboxBulk Upload (CSV), up to 5,000 rows

Google connects Google Workspace accounts only. Personal @gmail.com addresses are not supported, and cold email should send from your own domain anyway.

Plain guide

Sending infrastructure, explained without jargon.

What sending infrastructure is, why it decides how far cold email can scale, and how to grow it without hurting the mailboxes you already have.

  1. 01

    What sending infrastructure means

    Sending infrastructure is everything between your email and the reader's inbox that you control: the mailboxes you send from, the domains they live on, how much each one sends per day, and the domain your tracking links use. Good copy cannot fix weak infrastructure. If the mailbox sending your email has a poor reputation, the best message in the world still lands in spam.

  2. 02

    Why one mailbox is never enough

    Mail providers judge each mailbox by how it behaves. A person sends a handful of new emails a day, gets replies, and rarely bounces. A mailbox that suddenly sends hundreds of cold emails looks like a bot. So the safe way to send more is to send from more mailboxes, each at a modest pace, rather than pushing one mailbox to its limit.

  3. 03

    How daily limits work

    In FirstSales, each mailbox has a Daily Limit, the most emails it may send in a day. It can be set from 20 to 500, and starts at 50. With Auto-adjust on, which is the default, FirstSales tunes that number each night from the mailbox's sending health, lowering it when metrics slip and raising it as the mailbox recovers. An optional Send ceiling sets a hard top that Auto-adjust will never pass.

  4. 04

    How sends spread across mailboxes

    There is no separate rotation switch to set up. When you build a campaign, you choose which mailboxes send it. FirstSales spreads the campaign across those senders, and each one stays within its own daily limit. That means your total daily volume is roughly the number of senders times their safe limits. To double your volume, roughly double your warmed senders.

  5. 05

    Why domains matter as much as mailboxes

    Mailboxes on the same domain share that domain's reputation. Ten mailboxes on one domain are ten paths to the same risk. Spreading mailboxes across a few sending domains isolates the damage if one domain gets flagged. Each domain needs its own SPF, DKIM and DMARC records and its own tracking domain, or the extra volume simply gets filtered.

  6. 06

    What a tracking domain does

    When you track opens and clicks, your emails carry links and a small image that point somewhere. On a shared tracking domain, you share that domain's reputation with every other sender who uses it. A custom tracking domain is a subdomain you own, such as track.yourcompany.com, pointed at FirstSales with one CNAME record. It is separate from email authentication, and both matter.

  7. 07

    How to grow without breaking anything

    Grow in waves. Add new mailboxes, authenticate their domains, warm them up, and only then add them to a campaign as senders. Turn on Delivery Protection so a campaign pauses itself if bounces reach 5% or spam complaints reach 0.1%. Watch each mailbox's sending health as you go, and widen the pool only while the numbers stay clean.

Spread the risk

More domains, a smaller blast radius.

Mailboxes on the same domain share that domain's reputation. If the domain gets flagged, every mailbox on it feels it. Spreading mailboxes across a few domains keeps one bad day from stopping everything.

Nine mailboxes, one domain

One flag on the domain and all nine mailboxes carry it.

acme-mail.exampleFlagged

Nine mailboxes, three domains

One domain gets flagged. The other six mailboxes keep sending.

acme-mail.example

Flagged

acme-hq.example

Still sending

acme-team.example

Still sending

Sample layout. Every sending domain needs its own SPF, DKIM, DMARC and tracking domain, and every new mailbox needs warm-up before real campaigns.

Before you scale

A sending infrastructure checklist

Run through it each time you add mailboxes or widen a campaign's sender pool.

  • Each mailbox sends from your own domain, not a personal address
  • SMTP/IMAP mailboxes passed Test connection before saving
  • Every sending domain has SPF, DKIM and DMARC in place
  • Each sending domain has its own tracking domain, marked Verified
  • New mailboxes are warming up before they join a campaign
  • Daily limits are modest, with Auto-adjust left on
  • A Send ceiling is set if you want a firm upper bound
  • Mailboxes are spread across more than one sending domain
  • Delivery Protection is armed on every campaign
  • You add senders in waves and check sending health between them
“One of the best email outreach tools I have ever seen in my 9 years of business experience. It has solved the problem of email outreach for my cold emails.”
Santhosh K.Founder and CEO, small business · G2
Before and after

Running many mailboxes, the old way and with FirstSales

The same goal, sending at volume without burning domains, done two very different ways.

Per-mailbox tools or DIY

Spreadsheets, caps and surprises.

  • Pay per inboxEach extra mailbox raises the bill.
  • Add mailboxes one by oneFleets take an afternoon of clicking.
  • Guess which inbox sends nextA spreadsheet decides, and it drifts.
  • Push one mailbox harderThe cheap move is the risky one.
  • Shared tracking linksYour links share someone else's reputation.
  • Find out a mailbox died laterThe campaign just goes quiet.
With FirstSales

One place for every mailbox.

  • Unlimited mailboxesEvery plan, no per-mailbox fees.
  • Bulk Upload (CSV)Up to 5,000 mailboxes from one file.
  • Choose senders per campaignSends spread across the ones you pick.
  • Per-mailbox daily limitsAuto-adjust tunes them every night.
  • Your own tracking domainOne CNAME, SSL handled for you.
  • Reconnect alertsLost access shows up with a fix button.
Why teams switch

Sending infrastructure: FirstSales vs a typical tool

Many tools let you connect mailboxes. FirstSales is built for the moment you need many of them, without paying more for each one.

Sending infrastructure in FirstSales and in a typical cold email tool
What you getTypical toolFirstSales
Mailboxes per planVariesUnlimited, on every plan
WorkspacesVariesUnlimited
ProvidersVariesGoogle, Microsoft, any SMTP/IMAP
Bulk importVariesCSV, up to 5,000 rows
Daily limitsVariesPer mailbox, 20 to 500, auto-adjusted
Tracking domainVariesOne CNAME, SSL automatic
Lost accessVariesAlert and Reconnect Account
PriceVariesFrom $29/mo, no per-mailbox fees
Start your $1 trial
What people say

From people who use it

Real words from real users. No paid reviews.

“If you are looking to fix your sales pipeline, you should definitely try [it]. My open rate has increased drastically. The UI and UX are easy to understand, even for a beginner like me.”

Pooja Dhole

@ThisIsPoojaD

X

“One of the biggest pains in cold email is making sure that you have your DNS setup correctly. Firstsales has created a system to make sure you have done this correctly.”

Mike O

Trustpilot review

Trustpilot

“I've been using FirstSales.io for several months now, and I can confidently say it has revolutionized how I approach lead generation and customer acquisition.”

Paweł Stelmach

Small business owner

Trustpilot
Read all reviews

Go deeper

Questions,answered plainly.

Can’t find yours? Write to us.

01How many mailboxes can I connect?

As many as you need. Unlimited mailboxes and unlimited workspaces are included on every plan. Plans differ on monthly credits, not on how many mailboxes you connect.

02Which mailboxes can I connect?

Google Workspace and Microsoft accounts connect with a sign-in. Any other provider connects with SMTP and IMAP details. Personal @gmail.com addresses are not supported.

03Can I add many mailboxes at once?

Yes. In the SMTP/IMAP flow, use Bulk Upload (CSV). One file can hold up to 5,000 rows and must be under 5MB. A preview checks each row before anything is imported.

04How much can one mailbox send per day?

Daily Limit can be set from 20 to 500 per mailbox, with a default of 50. With Auto-adjust on, FirstSales tunes it every night from yesterday's sending health. Keep it modest and add mailboxes to grow.

05Is there a mailbox rotation setting?

No separate setting is needed. You choose which mailboxes send each campaign, and FirstSales spreads the sends across them, each within its own daily limit.

06What is a custom tracking domain?

A subdomain you own, such as track.yourcompany.com, pointed at FirstSales with one CNAME record. Opens, clicks and unsubscribes are then tracked on your own domain. SSL is set up for you.

07What happens if a mailbox loses access?

A Google or Microsoft mailbox shows an alert with a Reconnect Account button, and reconnecting keeps its daily limit, warm-up and signature. For SMTP/IMAP, run Test Connection and re-add it with new details if needed.

08Do new mailboxes need warm-up?

Yes. A new mailbox has no reputation yet. Turn on warm-up and let it build trust before you add it to a campaign as a sender.

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.

Start your $1 trial See pricing

$1 for 3 days · Cancel anytime · No contract

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 ↗