If your outbound open rates dropped and replies dried up, the problem is rarely the copy. Most of the time your emails are landing in junk, or not arriving at all. Inbox providers tightened the rules in 2024 and 2025, and senders who didn’t keep up are paying for it in silence – there’s no bounce, no warning, just fewer conversations.
This is the checklist we run when a client tells us “outbound has stopped working”. Work through it in order: each step depends on the one before.
1. Check your authentication: SPF, DKIM and DMARC
Google and Yahoo have required SPF, DKIM and DMARC for bulk senders since February 2024. Microsoft followed for Outlook.com, Hotmail and Live in May 2025, and now rejects non-compliant mail outright rather than sending it to junk.
- SPF lists every service allowed to send as your domain – including your CRM, your outreach platform and your marketing platform. A missing service means failed mail.
- DKIM signs each message. Every sending platform needs its own DKIM key set up on your domain.
- DMARC must exist (at least
p=none) and the From address must align with SPF or DKIM. Once everything passes, move top=quarantineso nobody can spoof you.
The thresholds are 5,000 emails a day, but don’t wait until you hit them. Providers judge your domain’s behaviour continuously, and authentication is the price of entry at any volume.
2. Stop sending cold email from your main domain
If your cold campaigns go out from the same domain as your invoices, proposals and day-to-day email, one bad week can damage all of it. Use separate sending domains for outbound, set up properly and warmed before they carry real volume. Keep your primary domain for the conversations that matter most.
3. Watch your spam complaint rate
Google expects complaints to stay below 0.3%, and treats under 0.1% as healthy. At cold-email volumes, a handful of “report spam” clicks a day is enough to cross the line. If complaints are high, the fix is targeting and relevance, not a new subject line.
4. Scale volume slowly – and only when the foundations are stable
Sudden jumps in volume are one of the clearest signals of a spammer. Ramp new domains gradually, cap daily sends per inbox, and only raise volume when placement and replies are holding steady. Scaling on unstable foundations makes every extra email do more damage.
5. Clean the list before you blame the campaign
Bounces tell providers you don’t know who you’re emailing. Verify addresses before sending, remove anyone who has bounced, and refresh data that’s more than a few months old. A smaller, accurate list beats a large, stale one every time.
6. Write for replies, not opens
Plain text, a clear reason you’re writing to this person, one simple question. Heavy HTML, tracking-heavy links and attachments all count against you. The best-performing cold emails read like one person writing to another – because that’s what they should be.
7. Measure placement, not just opens
Open tracking is now unreliable: privacy features pre-load images, and corporate filters click links before people do. Track inbox placement, bounce rate, complaint rate and – most importantly – replies and meetings. If you can’t see where your email lands, you can’t fix it.
Where to start
If you only do three things this week: confirm SPF, DKIM and DMARC pass for every platform that sends as you, move cold campaigns off your main domain, and check your complaint rate in Google Postmaster Tools.
If you’d rather have it looked at for you, our outbound email work starts with exactly this review, and Pulse+ campaign monitoring keeps watch on domain health and placement once campaigns are live. Book a demand health check and we’ll tell you what to fix first.
Sources: Google and Yahoo bulk sender requirements (Close); Microsoft enforces SPF, DKIM and DMARC (dmarcian).
