The short version
Sales and marketing teams increasingly own domains, mailboxes and sending volume directly, which means deliverability is now a GTM responsibility rather than something to hand off and forget. The baseline checklist: SPF and DKIM correctly configured and aligned, DMARC set to at least “quarantine” (not just “none”), a dedicated sending subdomain separate from your primary company domain, and a warm-up period of real, human-paced sending before any sequence tool ramps volume.
Skip this and even well-written outbound lands in spam, which quietly kills a campaign in a way that is invisible until you check inbox placement directly. Treat your sending domain’s reputation as an asset to protect, not a setting you configure once and ignore.
The setup order that avoids rework
Start with the domain, not the tool. Buy a secondary domain or use a subdomain for cold outreach, then publish SPF listing only your actual senders, enable DKIM signing, and publish a DMARC record beginning at p=none with reporting to a mailbox you read. Move to quarantine once reports show your legitimate mail passing alignment consistently.
Check each step with a free header test: send a message to a seed mailbox and read the authentication results for spf=pass, dkim=pass and dmarc=pass. One misaligned sender, such as a CRM sending on your behalf without DKIM, is enough to drag the whole domain’s reputation down, so inventory every system that sends from the domain.
Warm-up and volume discipline
Warm-up means real, gradual, human-paced sending. A sensible ramp starts at roughly 5 to 10 messages a day per mailbox and rises by a few each day over two to three weeks. Mix in conversations with genuine replies. Sending 50 cold emails from a brand-new mailbox on day one is the fastest way to a spam folder.
Keep per-mailbox volume conservative and spread load across several mailboxes only when each one is healthy. Randomise send times within working hours and avoid identical subject lines at scale. If a mailbox’s reply rate drops sharply while others hold steady, rest it for a week, rather than pushing volume through and burning the domain.
Content signals that trigger filters
Filters judge content as well as infrastructure. Keep first emails short, plain-text-like, with at most one link or none, and avoid tracking-pixel-heavy templates and image banners. Remove words such as “free” and “guaranteed”, urgency in capitals, and attachments. A subject like “Quick question on your Q3 hiring plan” performs better than a promotional headline.
Include a one-line opt-out: “If this isn’t relevant, tell me and I won’t follow up.” It reduces complaints, because an easy exit beats a spam-button click. Test every new template by sending it to seed accounts at a few providers before launching it to a list, and compare placement across them.
Worked example (illustrative)
A hypothetical team sends 600 cold emails a day from three mailboxes on its primary domain, then restructures sending over four weeks.
What changed: The copy did not change. Moving to a subdomain, fixing alignment, cleaning the list and capping volume per mailbox restored placement, and replies followed.
Do it: the steps
Tick them off as you go. Your progress stays on this device.
Traps to avoid
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Scaling volume by adding mailboxes instead of fixing the reasons people mark you as spam.
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Buying many domains and rotating them to dodge reputation. It treats a symptom, and providers increasingly detect this pattern.
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Ignoring DMARC reports. They show exactly which systems send as you, and the unknown ones are usually the cause of a surprise reputation drop.
What to track
- Inbox placement rate
- seed-test messages landing in the primary inbox divided by total sent; aim for above 85–90%
- Spam-complaint rate
- complaints divided by delivered; keep under 0.1% and never near 0.3%
- Bounce rate
- hard bounces divided by sent; pause the campaign and clean the list above 2%
Benchmarks are typical planning ranges, not guarantees. Calibrate to your own data.
Questions people ask
Should I use a separate domain or a subdomain for cold email?
Either protects your main domain, but a separate lookalike domain isolates reputation more strongly. A subdomain is simpler and keeps brand consistency, though reputation can partly bleed upward. Whichever you choose, never send cold outreach from the domain your customers and invoices use.
How do I know my emails are going to spam?
Use seed-inbox placement tests, Google Postmaster Tools for Gmail-heavy audiences, and watch for sudden drops in open and reply rates alongside steady send volume. Open rates alone are unreliable because of privacy proxies, so treat a reply-rate fall as the stronger signal.