Cold email deliverability checklist

A cold email deliverability checklist for B2B product sellers: SPF, DKIM and DMARC, a sending domain, mailbox ramp-up, volumes, list hygiene and bounces.

By the PromptLab team27 October 20267 min read

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Set up the domain you send from
Ramp up each new mailbox
Control volumes and gaps
Clean the list before you send
Write content that reads like a person
Handle unsubscribes and replies
Monitor bounces and reputation
The items people skip
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Cold email only works if it reaches the inbox. A coatings maker can write the perfect note to a regional distributor, but if it lands in spam, the distributor never knew it was sent. Deliverability is mostly set-up and discipline: prove to mail providers that you are who you say you are, send at a pace a real person would, email people who exist and make it easy to say no.

This checklist runs in the order you'd do it: domain first, then mailboxes, then sending habits, list, content, replies and monitoring. It is written for B2B teams that sell products and email buyers, distributors and purchasing managers.

Set up the domain you send from

Mail providers judge you first by your domain. Three DNS records tell them your email is genuine. Your IT person or domain host can add them in an afternoon.

SPF is a list of the servers allowed to send email for your domain. If an email claims to be from you but comes from a server not on the list, it looks forged.
DKIM adds a digital signature to each email. The receiving server checks the signature against a key in your DNS, which proves the message wasn't changed on the way.
DMARC tells receiving servers what to do when SPF or DKIM fails: let it through, send it to spam or reject it. It also sends you reports on who is sending as your domain.

Domain set-up

Add an SPF record that lists every service that sends as your domain (Google Workspace or Microsoft 365, plus any others)
Turn on DKIM signing in your mail provider and publish its key in DNS
Publish a DMARC record, starting with a monitoring policy, then tighten it once reports look clean
Decide whether cold email goes from a separate sending domain, such as a close variant of your main one
If you use a separate domain, give it its own SPF, DKIM and DMARC and a simple website that points to the main one

Note

A separate sending domain protects your main one. If cold outreach to new distributors goes wrong, the invoices and order confirmations your customers expect still arrive from the main domain. The trade-off is that a brand-new domain has no history, so it needs a slow start.

Ramp up each new mailbox

A mailbox that has never sent much, then suddenly sends hundreds of emails to strangers, looks like spam to Gmail and Outlook. Build volume slowly. There are two ways to do it: a warm-up network that trades emails with other mailboxes, or a gradual ramp-up of real sends. We explain both in what is email warm-up.

Mailbox ramp-up

Use real mailboxes with a real person's name, not noreply@ or info@
Add a signature with name, role, company, address and phone
Send normal day-to-day email from the mailbox for a while before outreach starts
Start cold sends low, for example 10 a day, and raise them week by week
Add more mailboxes to send more, rather than pushing one mailbox harder

Control volumes and gaps

Steady, human-looking sending is easier on your reputation than bursts. A rep doesn't send 50 emails in the same minute, so your campaigns shouldn't either.

Volumes and timing

Set a daily limit per mailbox and stay under it on every campaign combined
Spread sends across several mailboxes when the list is large
Leave a random gap of a few minutes between emails, not a fixed interval
Send inside business hours in the buyer's time zone, on working days
Pause and investigate if bounces or spam complaints jump, instead of pushing on

Clean the list before you send

Bounces hurt more than almost anything else. A list of distributors copied from a five-year-old trade-fair catalogue will be full of people who have left and addresses that no longer exist.

List hygiene

Remove addresses that bounced before, from any campaign or from normal email
Check that each contact still works at the company, especially on old lists
Remove anyone who has unsubscribed or asked not to be contacted, across every list
Exclude existing customers and current distributors from cold campaigns
Run new or bought addresses through an email verification service before the first send
Keep each campaign's audience to people with a real reason to hear from you, such as distributors that carry a related product line

Write content that reads like a person

Spam filters read content too, and so do buyers. A short, plain note from a named rep beats a designed newsletter for cold outreach. Our cold email templates for manufacturers follow these rules.

Content

Plain text or very light formatting, no large images or heavy HTML
One or two links at most, ideally to your own domain
No attachments on the first email: offer the technical data sheet instead
A subject line that describes the email, such as "Epoxy floor coatings for your Midlands customers"
Personalise beyond the first name: their region, product range or a trade show you both attended
Leave open tracking off on first sends if you can; opens are an unreliable signal because some mail apps load images automatically

Handle unsubscribes and replies

Making it easy to opt out keeps complaints down. A buyer who can't find a way out clicks "report spam", and that does real damage. Google and Yahoo's rules for bulk senders now expect authentication and one-click unsubscribe, and your local privacy laws may add their own requirements.

Unsubscribes and replies

Include an unsubscribe link, with one-click List-Unsubscribe in the email header
Honour an unsubscribe at once and across every campaign and mailbox
Stop the sequence for anyone who replies, whatever the reply says
Treat "not interested" as an unsubscribe for that campaign
Route replies to the rep who owns the account, the same day

Monitor bounces and reputation

Deliverability is not "set and forget". Check the numbers each week while a campaign runs.

Monitoring

Read the bounce list after every send day and remove hard bounces from the CRM
Watch the reply rate: a sudden drop on a known-good template often means spam folders
Look at DMARC reports for services sending as your domain that you didn't know about
Register your domain with Google Postmaster Tools to see how Gmail rates you
Send a test to a Gmail and an Outlook address you own and check where it lands

The items people skip

DMARC. SPF and DKIM get set up; DMARC is forgotten, and providers increasingly expect it.
The ramp-up on the second and third mailbox. Teams ramp the first one carefully, then add new mailboxes at full volume.
Company-wide unsubscribes. A distributor who opted out of one rep's campaign gets the next rep's.
Replies that stop the sequence. A buyer who said "send me a sample" then gets step three asking if they saw step one.

Our pick

Why PromptLab helps with deliverability

PromptLab's campaigns send from your own Gmail, Outlook or IMAP mailboxes, rotating up to 20 per campaign, with your signature. Daily limits per mailbox type are built in, and new mailboxes ramp up over three weeks (10 a day, then 20, then 30). Each campaign sends in the days and hours you choose, with a random gap between emails. A reply or a bounce stops the sequence, and the optional unsubscribe link includes one-click List-Unsubscribe and blocks that address company-wide. PromptLab has no warm-up network, so if you want one, pair it with a dedicated tool. Campaigns are on every plan from $11.99 per user per month. See sales automation.

Try PromptLab free14-day free trial. From $11.99 a user a month.

Once the basics are in place, follow the steps in how to run an email campaign to distributors.

Frequently asked questions

What are SPF, DKIM and DMARC in simple terms?

SPF lists the servers allowed to send email for your domain. DKIM signs each email so the receiver can check it is genuine and unchanged. DMARC tells receivers what to do when those checks fail and sends you reports.

Should I use a separate domain for cold email?

Many B2B teams do, to protect the main domain that carries invoices and order emails. Give the sending domain its own SPF, DKIM and DMARC, and ramp it up slowly because it starts with no history.

How many cold emails can I send per mailbox per day?

There is no single safe number, and it depends on the mailbox's age and history. Start low, around 10 a day for a new mailbox, raise it week by week and add mailboxes rather than pushing one harder. Apollo, for example, suggests starting at around 20 cold emails a day per mailbox and not going past 50 (checked 20 October 2026).

Why are my cold emails going to spam?

The usual causes are missing authentication, a new mailbox sending too much too soon, bounces from an old list, or heavy links and images. Work through this checklist in order and test with your own Gmail and Outlook addresses.

Does PromptLab have email warm-up?

PromptLab ramps up the daily volume of new mailboxes over three weeks, but it has no warm-up network. Tools such as Instantly, lemlist and Smartlead include warm-up networks if you need one.

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