Cold email deliverability: warm-up, daily limits and separate domains

Why cold email lands in spam and the rules that keep it in the inbox: authentication, gradual ramp-up, daily caps, sending windows, stopping on reply.

Illustration of an email climbing steps toward a thermometer, for cold email deliverability and mailbox warm-up

Cold email still works for B2B: a short, relevant note to the right person at the right company starts real conversations. It also fails quietly. A mailbox that sends too much too soon, or from a domain without proper authentication, slides into spam folders long before anyone notices. These are the rules we built EterMail's outreach around.

1. Keep cold email off your main domain

Your main domain carries your marketing email, your invoices and your team's day-to-day mail. If cold outreach hurts its reputation, all of that suffers. Send outreach from a separate domain (for example getyourbrand.com alongside yourbrand.com) with its own mailboxes. EterMail keeps outreach mailboxes and marketing senders apart, so one channel's reputation never affects the other.

2. Authenticate every sending domain

Mailbox providers check three DNS records before they trust a sender:

  • SPF lists the servers allowed to send for your domain.
  • DKIM signs each message so it can't be altered in transit.
  • DMARC tells receivers what to do when SPF or DKIM fail, and is now required by Gmail and Yahoo for anyone sending in volume.

When you connect a mailbox, EterMail checks its domain's SPF, DKIM and DMARC records and shows what is missing.

3. Ramp up slowly

A brand-new mailbox that suddenly sends hundreds of emails looks exactly like a compromised account. Start small and grow week by week. By default EterMail allows 10 emails a day in a mailbox's first week, adds 10 a day each week after that, and never exceeds the mailbox's daily cap (30 by default). You can change all three numbers per mailbox.

4. Spread the volume across mailboxes

If you need 300 cold emails a day, 10 mailboxes sending 30 each is far safer than one mailbox sending 300. EterMail rotates a sequence across the mailboxes you assign to it and respects each one's limit.

5. Send like a person

  • Business hours only, in the mailbox's time zone. EterMail's default window is 09:00–17:00, Monday to Friday.
  • Space messages out. Each mailbox waits at least three minutes between sends, randomised so the rhythm isn't mechanical.
  • Plain, short text. No heavy HTML, no attachments, at most one link in the first email.

6. Stop the moment they reply

Nothing damages trust faster than a "just following up" sent after someone already answered. EterMail reads each mailbox over IMAP, matches replies to the sequence, and stops all further steps for that prospect immediately. Out-of-office replies are recognised and simply push the next step back.

7. Make opting out easy and permanent

Every cold email should make it easy to say "not interested". When a prospect asks to be removed, EterMail stops the sequence and suppresses the address so the project never sends it cold email again.

8. Write for one reader

Relevance beats volume. EterMail's AI drafts a personalised opening line from each prospect's company information; you review the sequence and approve it before anything is sent. A reply rate that rises over time is the best sign that your deliverability is healthy.

Cost

Cold emails cost 5 credits each (about $5 per 1,000), or choose the $299/month Ultra plan, where cold email is not charged per send. Volume is still bounded by your mailboxes' safe daily limits. See pricing.