Cold Email Deliverability: What Decides It

What is cold email deliverability?

Cold email deliverability is how likely a message to someone you've never contacted is to land in their inbox, rather than in spam, junk or a promotions tab. Delivery is something else. A message counts as delivered once the receiving server accepts it during the SMTP conversation. Where it gets filed after that is a separate decision, made by Gmail, Microsoft or the recipient's own mail gateway. Neither you nor any sending platform controls that decision. What you do control are the signals the receiving server reads.

That's why the 'delivered' figure in your sending tool tells you so little. A message can be accepted and still end up in spam, and the sender never finds out. Open tracking doesn't answer the question either, because privacy features in some mail clients load tracking pixels automatically. Our piece on email open rate tracking limits explains why opens are a weak deliverability signal for cold senders.

What decides whether a cold email reaches the inbox?

Receiving servers weigh several signals together. Some are pass/fail checks, and others build up over weeks. The pass/fail checks are mechanical. The ones that build up over time are where most cold senders get into trouble.

• Authentication: SPF checks whether the sending server is allowed to send for the envelope domain. DKIM checks a cryptographic signature tied to a signing domain. DMARC requires at least one of them to pass and to align with the domain in the visible From header.
• Domain reputation: the history of mail signed by your domain, built from complaints, bounces and how recipients treat your messages. A new domain has no history, so filters treat it with caution.
• IP reputation: the history of the sending IP. With an email service provider like Brevo you often share IPs with other senders, which means your domain's own reputation counts for more.
• Bounces: repeated hard bounces of the 'user unknown' kind tell the receiver your list wasn't verified.
• Complaints: every 'report spam' click counts against your domain. Google's Email sender guidelines set a spam rate that senders should stay under, as measured in Postmaster Tools.
• Content and links: links to blocklisted domains, URL shorteners and heavy HTML with large images all push filter scores up.
• Volume pattern: a sudden jump from a quiet domain looks like a compromised account or a spam run.

How do I set up a domain for cold email?

Follow this order. Each step depends on the one before it. If you send before the authentication steps are live, you're building reputation on a domain that fails its checks.

1. 1 Choose the sending domain. Many senders keep cold outreach on a separate domain so complaints don't affect invoices and support mail on the main domain. The trade-off is that a new domain starts with no reputation and has to be warmed up.
2. 2 Publish a single SPF TXT record that lists every service sending for the domain. The SPF specification puts a hard cap on DNS lookups per check. If you go over it, you get a permerror, and receivers treat that as a failure. Two separate SPF records on one domain also cause a permerror.
3. 3 Turn on DKIM signing with your own domain as the signing domain (the d= value), not your provider's domain. That's the only way DKIM can align with your From address.
4. 4 Publish a DMARC record at _dmarc.yourdomain. Start with p=none and read the aggregate reports before you tighten the policy.
5. 5 Warm up. Start with a low daily volume and raise it step by step while you watch bounces and complaints.
6. 6 Verify the list before you import it. Remove role addresses and any address that has bounced before.
7. 7 Add a one-click unsubscribe through the List-Unsubscribe and List-Unsubscribe-Post headers, plus a visible opt-out line in the message itself.
8. 8 Check the legal basis for each recipient's country. German competition law is strict about advertising email sent without prior consent, and that includes B2B recipients. EU data protection law also requires you to inform people whose data you didn't collect from them directly.

Record-level detail for each of these steps is in our guide to DKIM, DMARC and SPF for cold email senders. The ramp-up schedule is covered in email warm-up: daily volumes and DNS setup.

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

No mailbox provider publishes a cold-email quota. The figures that get passed around are vendor rules of thumb. MailReach's deliverability guide (August 2026) recommends no more than 80 cold emails a day per sending address. OneAway's benchmark article (March 2026) puts it at 50 to 60 a day per mailbox. Treat these as starting points. Staying under them doesn't make you safe.

The real limit is how recipients react. A small batch to an unverified, poorly targeted list can do more damage than a larger one to verified, relevant contacts, because every bounce and spam report counts against you. Google's Email sender guidelines also set stricter authentication and unsubscribe rules for bulk senders to personal Gmail accounts. One approach does NOT work: spreading volume across lots of fresh domains to stay under every threshold. Each new domain starts with no history, and receivers can connect domains through shared tracking hosts, IPs and content.

What breaks cold email deliverability?

Failure	Cause	What you see	Fix
SPF permerror	Too many DNS lookups in the SPF record, or two SPF records on one domain	SPF fails even though the provider is listed	Merge everything into one record and remove includes you no longer use
DMARC alignment fails	DKIM is signed with the provider's domain instead of yours	Headers show DKIM passing and DMARC failing	Set up DKIM with your own domain as d=
Hard bounces pile up	Unverified list or outdated contacts	'User unknown' bounce responses	Verify before import and remove bounced addresses permanently
Sudden spam placement	Volume jump on a young domain	Messages accepted, no replies	Drop back to a lower daily volume and ramp up again
Rejection at Gmail	Missing or failing authentication	Bounces that name an authentication problem	Fix SPF or DKIM so DMARC passes
Link-based filtering	URL shorteners, or a link domain with a bad history	Spam placement despite clean authentication	Link to your own domain

For individual bounce codes and what each one means for your next send, see our guide to email bounce codes and causes.

Which tools check cold email deliverability?

Each of these tools answers a different question, and none of them shows where a real prospect's copy landed. They're compared here on the same three points: what they check, what they need from you and where they stop.

Tool	What it checks	What it needs from you	Where it stops
Google Postmaster Tools	Domain reputation, spam rate and authentication results for mail to Gmail users	Domain verified with a DNS TXT record	Only shows data once you send enough Gmail traffic, and only covers Gmail
Microsoft SNDS	Data on mail from your IP addresses to Outlook.com	Control of the sending IP	Of little use on an email service provider's shared IPs
MXToolbox	DNS records (SPF, DKIM, DMARC) and blocklist lookups	Your domain or IP	Checks configuration, not where mail is placed
mail-tester.com	Authentication, content and blocklist score for one test message	Sending one message to a generated address	One message to one test receiver, with no provider-specific placement
GlockApps	Placement of a test message across seed mailboxes at several providers	Sending to a seed list	Seed mailboxes have no history with you, unlike real recipients

Do sales follow-up emails affect deliverability?

Sales follow up email template: what keeps it out of spam?

A sales follow-up email template is reusable text for the second and later messages to a prospect who hasn't replied. Filters notice identical text going out at volume. A template sent word for word to hundreds of people starts to look like a bulk campaign. Write a frame you adapt for each recipient, keep links on your own domain and leave out attachments. Copy-ready versions are in our sales follow-up email template examples.

Follow up sales email: reply in the thread or send a new message?

A follow-up sales email sent as a genuine reply carries In-Reply-To and References headers, so mail clients group it with your first message and the recipient sees the context. Putting 'Re:' in the subject of a message that isn't a real reply misrepresents it, and the US CAN-SPAM Act prohibits misleading subject lines. Timing and threading are covered in cold email follow-up timing and threading.

Sales follow up email: when should I stop?

End a sales follow-up email sequence as soon as you get a hard bounce, an unsubscribe or any reply asking you to stop. Every message after that risks a spam report, and spam reports count against your sending domain. Under the GDPR, an objection to direct marketing ends processing for that purpose. Even where the law doesn't require it, a recipient who has ignored several messages is better treated as a closed contact than kept in rotation.

How EmailFlow OS sends: a EmailFlow OS product

EmailFlow OS is our own product, not one of the tools above. You record one video and upload it to EmailFlow OS. Then you connect your Brevo account and your sending domain, and import your prospect list into EmailFlow OS. EmailFlow OS creates a separate version of that single recording for each recipient, not one per company. Each version goes out from your own inbox, through your own Brevo account and your own sending domain.

What this means for deliverability is that there's no shared platform sender between you and your recipients. The reputation built by every send belongs to your domain. The SPF, DKIM and DMARC records you publish are the ones receivers check. Your Brevo account stays under your control. The receiving server still decides where each message lands, and the setup and warm-up steps above still apply. The mechanics are described on the EmailFlow OS home page.

Questions people ask

? What is a good cold email deliverability rate?

No mailbox provider publishes a benchmark. OneAway's March 2026 benchmark article calls 85 to 92 percent inbox placement good. The 'delivery rate' in your sending tool is a different measure. It only counts messages the server accepted and says nothing about inbox versus spam, so the two numbers can't be compared.

? Should I send cold email from my main domain?

Your main domain carries invoices, support and internal mail, and spam complaints from outreach count against that same domain reputation. A separate domain keeps the two apart. The downside is that it starts with no sending history, so it needs full SPF, DKIM and DMARC setup and a gradual warm-up before it can handle real volume.

? Does DMARC p=reject help cold email deliverability?

DMARC p=reject tells receivers to refuse mail that fails alignment. That protects your domain against spoofing, but it doesn't improve the reputation of mail that passes. Start with p=none, read the DMARC aggregate reports, and only tighten the policy once every legitimate sender aligns with your From domain.

? Why do my cold emails go to spam when SPF and DKIM pass?

Passing authentication only proves who sent the message. Placement also depends on domain reputation, complaint and bounce history, link domains and volume patterns. A young domain sending a sudden batch, or a link to a blocklisted domain, can land in spam even when every authentication check passes.