Cold email deliverability basics
Deliverability is infrastructure, not a copy trick. Authentication, warmup, volume and reply rate, in plain terms.
By Naman Jain, founder of SealrepPublished 17 October 2026
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The best-written email in the world does nothing from the spam folder. Deliverability is the foundation, and it is infrastructure, not a wording trick. Here is the short version practitioners and the mailbox providers agree on.
Authenticate everything
Set up SPF, DKIM and DMARC on every sending domain. Since February 2024, Google and Yahoo require authenticated mail from bulk senders, a one-click unsubscribe, and spam complaints kept low. These are no longer nice to have. They are the baseline that decides whether you reach the inbox at all.
Send from a secondary domain, never your main one
Use dedicated sending domains for cold outreach, kept separate from the domain you run your real business email on. If a cold domain’s reputation takes a hit, your primary domain and your real mail are untouched.
Warm the mailboxes, then keep volume low
New mailboxes need a ramp of roughly two to four weeks before they carry real volume. Even warmed, keep each inbox to a low daily number, around 20 to 40 cold sends a day; Hunter’s large analysis and most platforms put the degradation point not far above that. Stay under about 5,000 messages a day per sending identity to sit below the bulk-sender threshold Google and Yahoo watch.
Turn open tracking off
Open-tracking pixels inject a tiny image and an extra redirect into every send, and they correlate with worse placement. On cold email, turn them off. Measure replies instead, which is the number that actually matters.
Reply rate is the signal, bounce rate is the alarm
Mailbox providers increasingly read engagement. A positive reply looks like a real human conversation, which is the strongest possible signal that you are not a spammer. Verify your list so bounce rate stays at or below roughly 3 percent; a high bounce rate is the fastest way to wreck a domain’s reputation. Jeremy Chatelaine at QuickMail and the deliverability teams at MailReach and Folderly all land in the same place: optimise for genuine replies, watch bounce and complaint rates per domain, and pull back the moment either climbs.
The short list
Authenticate with SPF, DKIM and DMARC. Send from warmed secondary domains. Keep per-inbox volume low and total volume under the bulk threshold. No open tracking. Clean lists. Then let reply rate, not open rate, tell you whether it is working.
Questions people ask. Answered straight.
do I need SPF, DKIM and DMARC for cold email?
Yes. Since February 2024, Google and Yahoo require authenticated mail, one-click unsubscribe and low spam complaints from bulk senders. Without authentication, cold mail struggles to reach the inbox at all.
how many cold emails can I send per inbox per day?
Keep each mailbox to roughly 20 to 40 cold sends a day, even after warmup. Large analyses show placement degrades not far above that, so more inboxes at low volume beats a few inboxes pushed hard.
should I turn on open tracking for cold email?
No. Open-tracking pixels add an image and a redirect that correlate with worse inbox placement. Turn tracking off on cold sends and measure replies instead.
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