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Scale your sending volume safely

Grow daily send volume without burning domains: add more mailboxes to the sender pool, let auto-adjust and warm-up ramp each one, and keep delivery protection armed.

Tutorials
Deliverability
min read
10 min
steps
8 · Advanced

  1. Scale with mailboxes, not with one inbox's limit

    Total campaign volume comes from how many senders it uses. Adding mailboxes to the sender pool is the safe lever; pushing one mailbox past its daily limit is not.

  2. Stand up more mailboxes

    Add mailboxes (SMTP/IMAP one-by-one, or bulk-import a CSV) on fresh or aged sending domains. Spreading across more domains isolates risk further than piling more mailboxes onto one domain.

  3. Authenticate every domain

    For each sending domain, set up SPF, DKIM (Managed DKIM for credential mailboxes), DMARC, and a tracking domain. Un-authenticated volume gets filtered no matter how carefully you pace it.

  4. Warm up new mailboxes first

    Don't put real campaign load on a cold mailbox. Let warm-up build reputation; Auto-adjust keeps the daily limit in step with Sending health.

  5. Set per-mailbox limits sensibly

    Leave Auto-adjust on and add a Send ceiling you're comfortable with: the range is 20–500 per day per mailbox. Keep cold mailboxes low.

    Set per-mailbox limits sensibly

  6. Build the campaign's sender pool

    In the campaign's Email Accounts selector, add the warmed, authenticated mailboxes as senders: shown as “N/M selected.” Sending now spreads across all of them.

    Build the campaign's sender pool

  7. Arm Delivery Protection

    Turn on auto-pause (bounce 5% / spam 0.1%) so a scaled campaign stops itself if reputation slips: essential once volume is high.

    Arm Delivery Protection

  8. Ramp gradually and watch health

    Add senders in waves, watch each mailbox's Sending health and the campaign's bounce/spam rates, and only widen the pool while the numbers stay clean.

Pro tips

  • Volume = mailboxes × safe per-mailbox limit

    To double sends, roughly double your warmed senders: never double one mailbox's daily limit past what's safe (500 is the hard per-mailbox ceiling).

  • Spread across domains, not just mailboxes

    Ten mailboxes on one domain share that domain's reputation. Several domains isolate blast radius if one gets flagged.

  • Never add a cold mailbox straight to a live campaign

    Warm it first; auto-adjust and warm-up exist precisely so you don't hand-tune a ramp.

  • Scaling without auto-pause is gambling

    The one setting that saves you at volume is Delivery Protection: arm it on every campaign before you widen the sender pool.

Frequently asked questions

How do I send more emails per day?

Add more warmed, authenticated mailboxes to the campaign's sender pool. Volume scales with senders, not by raising one mailbox's limit.

Is there a mailbox rotation setting?

No: “rotation” just means selecting multiple sender mailboxes; FirstSales spreads sends across whichever ones you assign.

What's the per-mailbox limit?

20–500 emails/day, default 50, with Auto-adjust ramping it from Sending health. Scale by adding mailboxes, not by exceeding 500 on one.

Do I need to warm up every new mailbox?

Yes: a cold mailbox on real volume tanks deliverability. Warm it up first; auto-adjust respects warm-up health.

Does each domain need its own authentication?

Yes: SPF/DKIM/DMARC and a tracking domain per sending domain, or the extra volume just gets filtered.

How do I protect a high-volume campaign?

Arm Delivery Protection (auto-pause on bounce 5% / spam 0.1%) so it stops itself before reputation damage spreads.

Should I use one domain or several?

Several: spreading mailboxes across domains isolates the blast radius if one domain gets flagged.

How fast can I ramp?

In waves. Add senders gradually, watch each mailbox's Sending health and the campaign's bounce/spam rates, and widen only while metrics stay clean.

Deliverability

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 ↗