Why deliverability is your #1 revenue lever
Your sequence can have the best copy in the world — but if your email lands in spam, your pipeline is zero. Deliverability isn't an IT problem. It's a revenue problem.
Google and Microsoft now apply engagement-weighted reputation scoring at the mailbox level. This means a single sending domain that goes cold or triggers bulk-sender thresholds can suppress every email from your team — even reps who've never had a bounce.
DNS authentication: SPF, DKIM, DMARC
Authentication records tell receiving mail servers that your domain is who it claims to be. Without all three, your emails are rejected or silently dropped.
SPF (Sender Policy Framework)
SPF authorizes specific IP addresses and mail servers to send email on behalf of your domain. A correct SPF record looks like:
v=spf1 include:_spf.google.com include:sendgrid.net ~allCommon mistake: Having multiple SPF records. You can only have one. Merge all includes into a single record. Too many DNS lookups (more than 10) will cause SPF to fail.
DKIM (DomainKeys Identified Mail)
DKIM attaches a cryptographic signature to every outgoing email, letting the receiver verify the message wasn't modified in transit. Most sending platforms generate DKIM keys automatically — you publish the public key as a DNS TXT record.
selector._domainkey.yourdomain.com TXT "v=DKIM1; k=rsa; p=MIGf..."Use 2048-bit keys minimum. Rotate keys every 6–12 months.
DMARC (Domain-based Message Authentication)
DMARC ties SPF and DKIM together and tells receivers what to do when a message fails authentication. Start with p=none (monitoring only), then move to p=quarantine, then p=reject once you're confident.
_dmarc.yourdomain.com TXT "v=DMARC1; p=quarantine; rua=mailto:dmarc@yourdomain.com; pct=100"Inbox warming: how to do it properly
New mailboxes — and any mailbox that's been cold for more than 30 days — need to be warmed before sending outbound sequences. Sending at volume from a cold mailbox is the single fastest way to get your domain blacklisted.
Warmup principles
- Start slow: Begin at 5–10 emails/day per mailbox. Increase by ~20% per week.
- Positive engagement signals: Your warmup tool should be generating real opens, replies, and "marked as important" actions — not just sending volume.
- Don't mix warmup and outbound: Keep warmup traffic separate from your live sequences during the first 4 weeks.
- 30-day minimum: Treat a new mailbox as ready for full-volume outbound only after 4 weeks of consistent warmup with positive engagement rates above 30%.
Warmup targets
| Week | Daily volume per mailbox | Open rate target |
|---|---|---|
| Week 1–2 | 10–20 | ≥ 40% |
| Week 3–4 | 20–40 | ≥ 35% |
| Week 5+ | 40–80 | ≥ 30% |
Safe sending limits and mailbox hygiene
Gmail and Outlook apply bulk-sender rules that can suppress or throttle your mailbox without warning. Staying within safe limits protects your reputation long-term.
Recommended per-mailbox limits
| Provider | Safe outbound/day | Hard limit/day |
|---|---|---|
| Google Workspace | 60–80 | 500 (after warmup) |
| Microsoft 365 | 80–100 | 10,000 (rolling window) |
| Custom SMTP | 100–200 | Varies by provider |
Mailbox hygiene checklist
- ✓ Unsubscribe immediately when requested — never delay
- ✓ Bounce rate must stay below 2%. Scrub lists before import.
- ✓ Spam complaint rate must stay below 0.1% (Google's 2024 threshold)
- ✓ Use separate domains for outbound (e.g.
getacme.com) — protect your primary domain - ✓ Set up a catch-all on sending domains so hard bounces to non-existent addresses don't count against you
- ✓ Never purchase contact lists. Build or enrich from first-party signals.
Copy and content signals that trigger spam filters
Modern spam filters don't just scan for banned words — they evaluate patterns across your entire sequence to assess whether you look like a bulk sender.
What triggers spam filters in 2026
- Identical subject lines at volume. Even 100 copies of the same subject line triggers bulk detection. Personalize every subject.
- Heavy HTML / images / tracked links. Plain-text emails with one tracked link consistently outperform rich HTML for outbound.
- Aggressive spintax. Bulk-spinning the same template with token replacements is now detected by Gmail's language models.
- Missing unsubscribe. Since Google's February 2024 bulk sender mandate, every outbound email must include a one-click unsubscribe mechanism.
- Short time-between-steps. Sending step 1 on Day 1 and step 2 on Day 2 looks automated. Minimum 3 days between touches.
What good looks like
- ✓ Subject lines under 7 words, referencing something specific to the account
- ✓ Email body under 150 words for cold outreach
- ✓ One CTA per email, not three
- ✓ Plain text or minimal HTML (one signature image max)
- ✓ AI personalization that references a real signal — not generic flattery
Monitoring your sender reputation
You can't improve what you don't measure. Check these signals weekly — not monthly.
Tools to monitor
- Google Postmaster Tools — free, shows domain reputation, IP reputation, spam rate, and authentication pass rates for mail sent to Gmail
- Microsoft SNDS / JMRP — Microsoft's equivalent for Outlook/Hotmail deliverability signals
- MXToolbox Blacklist Check — scan your sending IPs against 100+ blacklists
- Mail-Tester.com — send a test email and get a deliverability score with specific fixes
Alert thresholds to act on immediately
| Signal | Green | Yellow — investigate | Red — pause sending |
|---|---|---|---|
| Spam complaint rate | < 0.08% | 0.08%–0.3% | > 0.3% |
| Hard bounce rate | < 1% | 1%–3% | > 3% |
| Domain reputation (Postmaster) | High | Medium | Low / Bad |
| IP on blacklist | 0 lists | 1–2 minor lists | Major list (Spamhaus) |
Recovering a damaged sender reputation
If your domain or IP is flagged, recovery is possible — but it takes 4–8 weeks of consistent positive signals. There are no shortcuts.
Recovery protocol
- Stop all outbound immediately from the affected domain and IPs.
- Identify the cause: Check Postmaster Tools, bounce logs, and complaint rates to find the spike that triggered the reputation drop.
- Clean your list: Remove all contacts with past bounces, spam complaints, or low engagement. Don't re-use a dirty list.
- Delist from blacklists: Submit removal requests to Spamhaus, Barracuda, and any other lists you appear on. Provide evidence the issue is resolved.
- Restart gradually: Begin re-warming at 5–10 emails/day. Use a warm list (existing customers or engaged contacts) first, not cold prospects.
- Monitor daily: Watch Postmaster Tools every day for 4 weeks. Reputation improvement is slow — don't accelerate until you see "High" domain reputation sustained for 2+ weeks.
If recovery from your primary domain proves too slow, consider spinning up a new subdomain (e.g. mail.acme.com) and warming it fresh while the primary recovers.
Wyzard handles all of this automatically.
From mailbox warmup and DKIM validation to list hygiene and reputation monitoring — WyzChannels keeps your deliverability healthy so you can focus on pipeline.
See Wyzard in action →