Cold email deliverability without risking your domain

Cold email lands in the inbox when the sending infrastructure looks trustworthy and the sending looks human. These are the rules every SLSBMB AI campaign runs on, and why each one exists.

Updated 2026-10-30 · Markdown

1. Never send cold email from your main domain

Your company domain carries your invoices, your team's email and your customers' trust. If a cold campaign earns spam complaints or bounces, that reputation can suffer. So we never send from it. Every campaign goes out from separate sending domains that look like yours, registered for outbound only, each with its own inboxes.

How SLSBMB does it: we register domains that resemble your brand and lead to your website or channel, so a recipient can see who is writing. Every sending domain carries four inboxes; the $800 Sending Engine entry is two domains and eight inboxes. The domains, servers, IP addresses and inboxes are ours, so every problem has one owner who fixes it.

2. Authenticate every domain

Receiving mail servers check whether a domain says who may send for it and whether messages are signed.

SPF lists the servers allowed to send for the domain.
DKIM signs each message so it can't be altered in transit.
DMARC tells receivers what to do with mail that fails those checks.

How SLSBMB does it: SPF, DKIM, DMARC and MTA-STS are set up for every sending domain before warmup starts, with matching server names and reverse DNS for every sending address. Inboxes sit on prepared IP addresses with strict density limits, at most 60 inboxes per physical IP, each with a fixed identity, so there are no random neighbours.

3. Warm new inboxes before the first cold email

A brand-new inbox that suddenly sends hundreds of emails looks like a spammer. Warmup builds a normal history first: a gradually growing volume of ordinary business correspondence between inboxes, which is delivered, opened and answered.

How SLSBMB does it: every inbox warms for about 21 days from the moment it exists, through AI-written business conversations between inboxes we operate, and progress counts only when control addresses at the major mail providers show the mail actually arriving. The first campaign emails go out around day 22, and only once the complete set of inboxes is connected and stable and every launch check is clear. Each inbox then starts at 2 campaign emails a day and adds 2 a day up to 15. Warmup keeps running alongside the campaigns. More in how our warmup works.

4. Keep daily volume per inbox low, and spread it out

Volume concentrated in a burst looks automated. Volume spread across the working day at a modest rate looks like a person.

How SLSBMB does it: at most 15 campaign emails per inbox per sending day, spread through the sending window instead of sent in bursts. Google Workspace technically lets one user send up to 2,000 emails a day, but trust works differently, and Google names no safe number: 15 is our own limit, set by experience. More volume comes from more domains and inboxes, which is what a larger Sending Engine budget buys; each inbox keeps the same limit.

5. Email verified business addresses only

Bounces are one of the strongest negative signals a sender can produce.

How SLSBMB does it: contacts count only once their business email is verified as deliverable, and we never email private inboxes. In a snapshot of our sending on 27 October 2026, about 1.7% of unique addresses bounced as invalid. Not every failed delivery is a bad contact — blocks, sender reputation, full mailboxes and network failures happen too — so we store the reason for every failure: a contact problem is fixed in the data, a mail problem in delivery.

6. Write plain text, like a person

How SLSBMB does it: campaigns are plain-text sequences — no tracking pixels or heavy formatting — with the sender's company and physical address and an opt-out line. The wording of every email varies from recipient to recipient while the meaning stays the same, so providers never see thousands of identical messages.

7. Make it easy to say no, and respect it forever

How SLSBMB does it:

Every email carries a one-click unsubscribe link on the sending domain.
Anyone who unsubscribes, complains, replies with hostility, hard-bounces or asks not to be contacted is blocked for good.
An ordinary reply, even "not now", stops that person's follow-ups at once.

8. Read every reply

Auto-replies, bounces and unsubscribes must be handled quickly, and interested people must not wait.

How SLSBMB does it: every reply is read and sorted. Junk and automatic replies are filtered out, and the people who want to talk land in your SLSBMB AI inbox and CRM.

9. Send the whole volume, smoothly

Bursts look automated, and catching up on a missed day with a burst is just as bad as losing the volume.

How SLSBMB does it: everything due today goes out today, spread evenly through the remaining sending window, at uneven intervals so the next send can't be predicted. If the window shrinks, the intervals shrink, not the volume; an email that truly doesn't fit moves to the next allowed window instead of a catch-up batch. Sending runs on working days in the campaign's time zone. One logical email is one person, one step of the sequence and one planned time, sent exactly once: after a crash or a dropped connection the system continues the same operation and never sends a duplicate.

How we watch delivery

Mail providers change their rules without notice, so we keep watching. Control addresses at the major providers show which folder our mail lands in, "sent" means the receiving server accepted the email, and failures are visible as failures. When a warmup or delivery check turns red, the system starts a repair session itself, finds the cause and checks that delivery recovered.

Frequently asked questions

Why do the first cold emails go out on day 22?

New inboxes need about three weeks of warmup before cold email lands in the inbox instead of spam. We warm yours for 21 days, so the first campaign emails go out around day 22.

How many cold emails can one inbox send a day?

We send at most 15 campaign emails per inbox per sending day. To send more, add domains and inboxes instead of pushing each inbox harder.

Will cold email hurt my company domain?

Not if you never send it from your company domain. SLSBMB sends only from separate, authenticated and warmed sending domains.

Do I need SPF, DKIM and DMARC for cold email?

Yes. All three should be set up on every sending domain before you send; Google's email sender guidelines require them of bulk senders. SLSBMB configures them, plus MTA-STS, for every domain it registers.

Can I use my own inboxes or buy pre-warmed ones?

Not in the Sending Engine. We don't know the history of inboxes we didn't build, and one dirty history can hurt the shared infrastructure every client sends from. A "pre-warmed" inbox is a label, not a history you can check.

What bounce rate is acceptable for cold email?

As low as verification can make it. Bounces are one of the strongest signals that a sender uses junk lists. In a snapshot of our own sending on 27 October 2026, about 1.7% of unique addresses bounced as invalid.