Authentication, list hygiene, IP warmup, reputation monitoring — the complete 2026 checklist for inbox placement.
Add a TXT record to your DNS: v=spf1 include:amazonses.com ip4:YOUR.IP -all. List every IP and service allowed to send on your domain. A -all hard-fail is correct — ~softfail invites spoofing.
Generate a 2048-bit RSA keypair. Publish the public key as a TXT record. Your ESP signs outgoing messages with the private key. DKIM proves the message was not tampered with in transit.
Start with p=none to monitor, move to p=quarantine, then p=reject. Add rua= for aggregate reports. Gmail and Yahoo have required DMARC for bulk senders (>5K/day) since February 2024.
Once DMARC is at p=quarantine or p=reject, add a BIMI record with a verified logo. Google and Yahoo show your brand mark in the inbox — improves open rates by 10-20% according to independent studies.
Run your list through BounceZero before every campaign. Remove Invalid, Disposable, and Role addresses. This reduces bounce rate from 5–15% (typical unverified) to under 0.3%.
Collect email addresses via confirmed double opt-in. One-click unsubscribe links in every message. Never use purchased, scraped, or rented lists — they are the single largest cause of blacklisting.
Hard-bounced addresses must go onto a global suppression list the moment the bounce is received. A suppression list applied only per-campaign is not sufficient — addresses re-appear from CRM syncs.
Contacts who have not opened or clicked in 6+ months are more likely to mark as spam than to convert. Run a re-engagement campaign, then suppress non-responders. Removing disengaged contacts improves open rate and lowers complaint rate.
Start at 500–1,000 emails/day on a new IP and increase 20–30% daily. Send to your most engaged subscribers first (recent openers). Hitting volume too fast triggers ISP throttling and 4xx soft bounces even to valid addresses.
Google's Postmaster Tools shows your spam complaint rate in real time. Above 0.1% triggers filtering; above 0.3% causes bulk folder placement. Remove complainants immediately via FBL.
Large volume spikes after quiet periods look like compromised accounts to ISPs. If you're increasing send frequency or list size, ramp gradually — do not triple volume overnight.
Changing From addresses frequently resets your domain reputation. One primary sending domain per brand. Use subdomains (news.example.com) to isolate marketing from transactional.
Monitor domain reputation (High/Medium/Low/Bad) and spam rate daily. Set up email alerts for reputation changes. A drop from High to Medium needs investigation within 24 hours — it becomes Low within days without action.
Register your IPs at sendersupport.olc.protection.outlook.com. SNDS shows green/yellow/red IP reputation scores. Red means active blocking — contact Microsoft Postmaster support immediately.
Check your sending IPs against Spamhaus ZEN, Barracuda, and URIBL weekly. Use BounceZero's free IP Blacklist Checker. A listing left unresolved for more than 48 hours compounds.
Register for feedback loops with Yahoo, AOL (Verizon Media), and Comcast. Receive complaint reports and suppress complainants within 24 hours.
Authentication (SPF, DKIM, and DMARC) is foundational — without it, major ISPs reject or junk your messages regardless of content. After authentication, list quality (low bounce rate and spam complaint rate) has the biggest impact on inbox placement.
Set up Google Postmaster Tools to monitor Gmail inbox vs spam placement rate. Use Microsoft SNDS for Outlook/Hotmail. Send test messages to seed inboxes across providers. Monitor open rate trends — a sudden drop usually signals bulk folder placement.
There is no single threshold — ISPs use rolling windows and relative scoring. However, sustained bounce rates above 2% damage domain reputation, above 5% can trigger IP-level blocks, and above 10% on a large send can result in DNSBL listing (Spamhaus, Barracuda). Keep below 0.5%.
Verify before every campaign and re-verify any segment not mailed in 90+ days. Run a full list clean every 6 months. Corporate lists need more frequent cleaning because professional email addresses expire 30-90 days after employees leave.
DMARC prevents spoofing and tells ISPs how to handle mail that fails SPF/DKIM alignment. A DMARC policy at p=reject shows ISPs you are a responsible sender, which improves reputation scoring. Gmail and Yahoo now require DMARC for bulk senders.
100 free credits. Clean your list before your next campaign.
Start FreeDeep-dive guides on how email verification and inbox placement work
How the 5-stage pipeline checks a mailbox without sending email
The RCPT TO handshake explained — codes, catch-alls, limits
Why domains accept everything and how ML classifies deliverability
Temp addresses, how to detect them, and why they matter
Hard vs soft bounces, SMTP codes, and how to fix them
Get from 5-15% to under 0.5% in 6 steps
Follow BounceZero