How to make sure your leads actually see your cold email

A verified list only pays off if the email lands in the inbox. Whether it does depends on five things you control: which domain you send from, how much each mailbox sends, whether the mailboxes are warmed, whether you check placement every day, and how fast you stop when it slips. Get those right and the leads you paid for see your message. Get one wrong and a perfect list goes to spam.

The five rules at a glance

1. Send from dedicated domains, never your main one.
2. Keep volume small: 3 mailboxes per domain and 16 emails per mailbox per day on Google, 400 a day per 25-mailbox tenant on Microsoft.
3. Warm every mailbox before outreach starts, and keep warming while it runs.
4. Check placement every day.
5. Pause a domain at the first spam spike and rest it for about nine days.

1. Send from dedicated domains, never your main one

Mailbox providers judge reputation by domain, so cold email should never touch the domain your company runs on.

Your main domain carries invoices, support replies, password resets and every conversation your team has with customers. If cold outreach damages its reputation, all of that lands in spam with it. A separate sending domain caps the damage: if one gets burned, you retire it and the business keeps working.

Buy lookalike domains that a prospect will recognize as yours, such as getacme.com or acmehq.com, and point their websites at your main site. Then set up authentication on each one before it sends anything:

• SPF and DKIM, so providers can confirm the mail is yours.
• DMARC, at least p=none to start. Google requires it for anyone sending 5,000 or more messages a day to Gmail accounts, and Microsoft requires SPF, DKIM and DMARC for domains sending more than 5,000 a day to Outlook.com addresses.

Treat these as the floor, not the finish line. Authentication tells a provider who sent the mail. It says nothing about whether recipients want it.

2. Keep volume small

Volume is where most domains break. Spread sending across many mailboxes and domains, and keep each one well under the level that draws attention.

The numbers that hold up in October 2026:

Count follow-ups in those numbers, not just first emails. A sequence of four steps still sends four emails.

To scale, add domains and tenants instead of pushing more through the ones you have:

Two habits keep this safe:

• Raise volume in small steps. Never lift a domain's daily volume by half or more in one go. A sudden jump on a young domain is the most common way we see domains end up in spam.
• Don't send cold email from a domain that hasn't been warmed. New domains and mailboxes need about three weeks of warming before they carry full volume (rule 3).

3. Warm every mailbox, before and during outreach

Warming builds the history a new mailbox lacks: mail that gets opened, replied to and rescued from spam. Keep it running after outreach starts, because it balances the low engagement of cold mail.

Not all warmup helps. Two things decide whether it does:

• Does the warmup mail look like real email? Many tools swap templated or irrelevant messages between mailboxes. Google and Microsoft detect those patterns easily, and detected warmup builds nothing. Warmup should read like the sender's own mail: relevant threads that go back and forth, with real engagement.
• Where do the warming mailboxes live? Reputation with Google and Microsoft is earned with Google and Microsoft mailboxes. A pool of SMTP mailboxes, often on IPs far from where your buyers are, builds little reputation where it counts. Ask your tool what share of its network is Google Workspace and Microsoft 365, and where those accounts are.

At MailStrike, each mailbox gets an AI agent that writes like the sender. The network is 100% Google and Microsoft accounts, 95% of them in Europe and North America. Whichever tool you use, ask it those two questions.

4. Check placement every day

A domain rarely goes from inbox to spam in a single day, but it can within a week. Daily checks catch the slide while it is still small.

Watch these every morning, per domain:

• Placement tests. Send to test inboxes at Gmail and Outlook and see whether the message lands in the inbox, the Promotions tab or spam. This is the only direct view of where your mail goes.
• Google Postmaster Tools. Google requires a spam rate below 0.3% and sets 0.1% as the target. Check it for every sending domain.
• Bounces. A rising bounce rate usually points to the list, not the domain. Verify contacts before they enter a sequence, and remove any address that bounces.
• Replies per domain. If one domain's replies fall to zero while the others hold steady, its mail is probably landing in spam.

Doing this by hand across twenty domains takes most of a morning. A deliverability tool like MailStrike runs the checks and tells you each day which domains need attention and what to change.

5. Pause at the first spam spike, and rest the domain

When a domain starts landing in spam, stop its campaigns that day. Every send after the spike digs the hole deeper.

The steps:

1. Pause outreach on the affected domain as soon as placement tests or replies show spam rising. Leave the other domains running.
2. Rest it, with warming still on. On average a domain needs about nine days with no campaign mail while warming rebuilds its engagement. MailStrike runs this repair automatically, and you watch placement recover in the daily checks.
3. Resume at low volume once placement is back in the inbox, then step up gradually (rule 2).

Keep a few warmed spare domains ready, so a paused domain doesn't stop the campaign. Sending moves to the spares while the paused domain recovers.

Checklist

• Cold email goes out from dedicated lookalike domains, never the main domain
• SPF, DKIM and DMARC are set on every sending domain
• Google: 3 mailboxes per domain, 16 emails per mailbox per day, follow-ups included
• Microsoft: 25 mailboxes per Azure tenant, 400 emails a day in total
• Every mailbox warmed for about three weeks before outreach, and warming left on
• Placement, spam rate, bounces and replies checked daily, per domain
• A domain pauses at the first spam spike and rests for about nine days
• Warmed spare domains ready to take over

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