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Provider specific tactics

provider-specific-tactics.md

Provider-Specific Tactics

How to diagnose and fix deliverability issues at each major mailbox provider and spam filter, based on experience managing large-scale sending operations.

Gmail

How Gmail Thinks

Gmail uses correlation-based filtering — it connects multiple data points to identify coordinated operations. It's not just looking at one signal; it's looking for patterns.

Gmail's strategy: "Make it unprofitable, not impossible." They don't block everything outright — they make spamming so costly in terms of blocked mail and wasted resources that legitimate senders optimize while bad actors give up.

Correlation Points Gmail Watches

  • Physical business addresses shared across domains
  • Web hosting IPs shared across "different" brands
  • Similar domain naming patterns
  • Sender identity mismatches (display name vs. email address)
  • Similar or identical content sent from different domains
  • Lack of consistent branding across sends

Gmail-Specific Warmup

  • Start at ~200 emails/day for campaigns
  • Never exceed 4x previous day's opens
  • Domain reputation in Google Postmaster Tools is your primary signal
  • Reputation levels: High → Medium → Low → Bad
  • Moving from Low to High takes weeks of consistent positive signals

Gmail-Specific Fixes

  • Content filtering: Address all correlation points. If multiple domains share infrastructure markers, Gmail treats them as one sender.
  • Domain reputation "Bad": Full warmup restart needed. Consider whether the domain is recoverable or if starting fresh is more practical.
  • Low engagement: Gmail heavily weights engagement. Sending to inactive subscribers actively damages your reputation there.

Microsoft (Outlook / Hotmail)

How Microsoft Differs

Microsoft tends to be more aggressive with blocking than Gmail. Where Gmail might spam-folder your emails, Microsoft might outright reject them.

Microsoft-Specific Warmup

  • Start very low: 25 emails/day when recovering from damaged reputation
  • Never exceed 4x previous day's opens
  • Microsoft separates Outlook.com and Hotmail — track both independently
  • Recovery is often slower at Microsoft than Gmail

Microsoft-Specific Issues

  • Outages affect senders: Microsoft's own outages can cause mass bounces. The ESP should detect this and pause sending: "If everybody starts getting blocked at Microsoft because it went down again, we should pause sending and not just bounce a gazillion emails off of Microsoft's infrastructure."
  • Aggressive gray-listing: Microsoft uses gray-listing (code 400 soft bounces) extensively. Legitimate senders retry and get through; spammers don't. Understanding this behavior is critical — it inflates apparent soft bounce rates for legitimate senders. Never treat graylisted soft bounces as a dirty list: retry them, and only treat what still fails after three attempts across 72 hours as a hard bounce. Suppressing on the first soft bounce at Microsoft deletes valid, reachable addresses.

Microsoft-Specific Fixes

  • When Microsoft blocks: 48-hour pause from that IP, then restart at minimal volume
  • New IP may be preferable to rehabilitating a blocked one
  • Track Hotmail and Outlook.com as separate segments during warmup

Yahoo

How Yahoo Differs

Yahoo is generally more forgiving than Gmail or Microsoft. Good news: easier to recover. Bad news: people sometimes use Yahoo success as false confidence about overall deliverability.

Yahoo-Specific Warmup

  • Start at ~50 emails/day when recovering
  • Never exceed 4x previous day's opens
  • Yahoo performance recovering doesn't mean Gmail performance is fine

Yahoo-Specific Tactics

  • Yahoo's engagement weighting is lighter than Gmail's
  • Still important to segment by engagement, but Yahoo gives more room for recovery
  • Watch for Yahoo-specific spam folder placement vs. blocks — they behave differently

iCloud / Apple Mail

The iCloud Signal

iCloud/Apple Mail open rates below 10% indicate severe inbox placement problems. Because Apple Mail Privacy Protection inflates open rates, genuinely low iCloud opens mean almost nothing is being delivered to inbox.

iCloud-Specific Considerations

  • Apple MPP (Mail Privacy Protection) pre-fetches images, which inflates open rate numbers
  • If you're seeing sub-10% opens at iCloud despite MPP inflation, the actual engagement is dramatically worse
  • iCloud placement is heavily reputation-dependent
  • Do not use the 4x-opens ramp here — MPP inflation makes it unsafe. Use a fixed daily schedule and watch bounces and delivery instead
  • Recovery approach follows the standard warmup playbook but with extra attention to engagement quality

ProofPoint

How ProofPoint Works

ProofPoint is a corporate spam filter (not a mailbox provider). It protects enterprise email systems — so when you're sending to business addresses at companies using ProofPoint, different rules apply.

ProofPoint-Specific Issues

  • Sending rate sensitivity: "The rate at which they were sending for one customer into the ProofPoint spam filter was not working. It was generating huge numbers of soft bounces."
  • IP-level blocking: ProofPoint blocks at the IP level. Getting delisted requires contacting ProofPoint directly.
  • Throttling requirement: The ESP's MTA must throttle sending rate to ProofPoint-filtered domains. Sending too fast = automatic soft bounces.

ProofPoint-Specific Fixes

  • Get the IP delisted from ProofPoint's blocklist directly
  • Implement MTA-level throttling for ProofPoint-filtered domains
  • Reduce sending volume to ProofPoint destinations during recovery
  • ProofPoint soft bounces are often rate-related, not reputation-related — distinguish between the two

SpamHaus

What SpamHaus Does

SpamHaus maintains blocklists that many mailbox providers and spam filters reference. A SpamHaus listing can cascade across multiple providers simultaneously.

Automatic SpamHaus Listing Triggers

  • HELO/rDNS mismatch: "If the HELO, the server announcement that comes through the SMTP connection, doesn't match the IP's reverse DNS — that is an automatic SpamHaus listing. If you hit enough networks with it."
  • Spam trap hits: Sending to SpamHaus-maintained spam traps
  • High complaint rates: Excessive spam reports from multiple sources

SpamHaus Diagnosis

Use the free SpamHaus domain reputation checker to check:

  • Negative reputation scores
  • Infrastructure quality assessment
  • Domain creation dates (new domains are higher risk)
  • Whether multiple domains share the same IP address

SpamHaus Delisting

  • Fix the root cause first — delisting without fixing the cause results in re-listing
  • Submit delisting request through SpamHaus portal
  • Provide evidence of remediation steps taken
  • Monitor closely after delisting — re-listing happens fast if the problem recurs

Cross-Provider Strategy

The Segment-by-Provider Approach

During any warmup or recovery, segment sending by mailbox provider. Each provider has different:

  • Rate tolerances
  • Engagement weighting
  • Block vs. spam-folder behavior
  • Recovery timelines

Real-world example of segment management during warmup: "I literally one time had to create eight separate segments for the different mailbox providers and spam filters and then literally update those every day and say okay, well today I sent to the last one to three days of engaged people at ProofPoint, Microsoft, Gmail, Hotmail, whatever."

Reading Provider Signals Together

  • All providers declining: Likely a content or data quality issue
  • One provider declining, others stable: Provider-specific throttling or reputation issue
  • Sudden drops everywhere: Authentication failure, DNS change, or SpamHaus listing
  • Gradual decline: Engagement erosion — probably sending to too many inactive contacts

The 4x Rule

Where opens are trustworthy: "Never send more than 4x previous day's opens."

If you sent 100 emails yesterday and got 25 opens, today's maximum is 100 emails (4x25). This prevents over-sending to unengaged audiences and naturally scales volume as engagement improves.

The Apple exception. Do not ramp on this rule at iCloud or Apple Mail. Mail Privacy Protection pre-fetches images, so a large share of those opens are machines, not people. Multiplying an inflated number authorizes volume no human asked for. Ramp Apple on a fixed schedule instead, and judge it on delivery and bounce behavior. The same caution applies anywhere else opens are proxied or prefetched.