Issue 1: Sender authentication (SPF, DKIM, DMARC alignment)
Symptom: emails landing in spam at one provider but not others, or DMARC reject reports arriving in the inbox you set as your rua address. Root cause: SPF or DKIM is not aligned to your sending domain, or your DMARC policy is still at p=none and never tightened. The 2024 Gmail and Yahoo bulk sender requirements (announced October 2023, enforced from February 2024) made DMARC enforcement table stakes for any sender pushing more than 5,000 messages per day to those providers; senders without aligned authentication are now rejected outright, not filtered. Fix: configure DKIM signing in Braze (the docs.braze.com 'Email setup' page walks through the DNS records, including the selector and the 2048-bit key), align the SPF return-path domain with your Friendly-From header so DMARC sees alignment under relaxed mode, then move DMARC from p=none to p=quarantine after 30 days of clean aggregate reports, then to p=reject after another 30. The M3AAWG sender best practices document (free PDF, version 3.0 published 2023) is the industry reference; Google Postmaster Tools shows the live authentication health per recipient domain on a 24-hour delay.
Issue 2: IP warm-up (or the lack of it)
Symptom: a new dedicated IP sends fine to 1,000 recipients, then deliverability collapses at 10,000. Root cause: inbox providers throttle unknown IPs by volume because they have no reputation history to score against, so they assume the worst until the IP earns trust. You have to warm the IP up by ramping send volume gradually over four to six weeks. Fix: follow a published warm-up schedule. The Braze docs page 'IP warm-up best practices' has one; the M3AAWG warm-up guidance has a more conservative version. Typical ramp: start at 50 per day per major provider (Gmail, Yahoo, Outlook, AOL), double daily for the first week, target your steady-state volume by day 30. Send only to your most-engaged users during warm-up (recent openers, recent clickers) because their positive engagement teaches the provider that mail from this IP is wanted. If you are migrating to Braze from another ESP, request a parallel warm-up plan with your Braze CSM and keep some traffic on the old IP until the new one is warm. The r/EmailDeliverability subreddit has working warm-up schedules from senders at every scale.
Issue 3: Complaint rate above 0.3 percent
Symptom: Gmail throttles your domain, Yahoo sends to Promotions tab and then to spam, Outlook flat-out blocks. Root cause: more than 0.3 percent of recipients are hitting the spam-report button, which Gmail and Yahoo treat as the formal threshold under their 2024 bulk-sender requirements. 0.1 percent is the safe zone, 0.3 percent is the warning, and anything north of 1 percent is a red flag that will produce global filtering across most major providers. Fix: audit acquisition cohorts (paid traffic complaint rate is usually 3 to 5 times organic in our experience), tighten frequency caps for low-engagement segments (anyone who has not opened in 60 days should be on a much lower cadence), and make the List-Unsubscribe header and the unsubscribe link in the footer genuinely prominent. The 2024 RFC 8058 one-click unsubscribe is now a hard requirement for bulk senders to Gmail and Yahoo. The IAB Email Council guidelines and the M3AAWG abuse-complaint guidance are the canonical references; r/EmailMarketing has weekly threads on complaint-rate recovery patterns and the cohort-by-cohort analysis they ran to find the source.
Issue 4: Hard bounce accumulation
Symptom: bounce rate climbing month over month, sender reputation tanking visibly in Postmaster Tools. Root cause: invalid addresses entering the list (typos at signup, role-based addresses such as info@ or sales@, abandoned mailboxes that providers turn into spam traps after 12 months), and Braze not removing them aggressively enough because someone disabled the default suppression. Fix: enable Braze's automatic hard-bounce suppression (the docs.braze.com 'Hard bounce management' page describes the SubscriptionState transitions). Add an email validation step at signup (Kickbox, ZeroBounce, NeverBounce, or Hunter; pricing is roughly $5 per thousand validations and the payoff is immediate). Quarterly: re-validate any address that has not opened in 180 days, because that is where recycled spam traps live. The Validity (formerly Return Path) Sender Score guide explains the bounce thresholds at major providers; 2 percent total bounces is the soft ceiling at Gmail, and Outlook reacts more harshly to hard bounces specifically.
Issue 5: Suppression-list drift
Symptom: a user who unsubscribed in Braze last month receives a 'related' email this month from a different campaign, because your CDP did not sync the suppression back and an audience export rebuilt the user into a segment. Root cause: the unified suppression list lives in Braze, the activation audiences live in the CDP, and the two diverge unless you reconcile on a schedule. Every fresh audience export that is not gated by the Braze unsubscribe list will recycle the unsubscribed user. Fix: nightly reconciliation job that pulls Braze's email unsubscribe list via /email/unsubscribes (the REST API page in the Braze docs describes the pagination and rate limits) and merges it into the CDP suppression. The r/Braze and r/marketingautomation subreddits have multiple 'suppression sync' threads; the working pattern at every scale is to make Braze the system of record for unsubscribe state and force the CDP to honour it on every export. This issue is the silent killer; most teams do not see it until a regulator or a 'why am I still getting this' complaint surfaces.
Issue 6: Send-rate spikes
Symptom: a single campaign sends five million emails in 20 minutes, inbox providers see the volume spike from a previously low-volume IP, deliverability for the next 48 hours collapses across the IP pool. Root cause: the sending pattern looks like spam (huge volume, then silence), which is exactly the historical signature of compromised IPs. Fix: use Braze's Send Rate Controls to throttle big campaigns over hours, not minutes. The smoothing is barely visible to the end user (a few hours of send window) and is the difference between a healthy reputation and a 48-hour penalty. Mix transactional and marketing traffic on the IP pool so the volume looks steady to receivers, with transactional providing the daily baseline and marketing layering on top during sends. The Word to the Wise blog (Laura Atkins) and the r/EmailDeliverability community both publish working throttling schedules for senders at every scale.
Issue 7: Content scoring and spam-trigger words
Symptom: subject lines you tested internally hit the spam folder at Gmail or Outlook. Root cause: inbox providers run machine-learning content classifiers on every email, and yours hit a feature combination flagged as commercial-promotional. The classifier is not a simple keyword filter any more; it is a learned model that scores layout, link density, image-to-text ratio, sender history, and language together. Fix: avoid the obvious triggers (excessive capitals, multiple exclamation points, the literal word 'FREE' in subject lines, urgent language combined with countdown timers), keep the text-to-image ratio above 60 percent text (Gmail explicitly penalises image-only emails), and use Litmus or Email on Acid to pre-screen against major filters before send. Mailchimp's 'spam filter triggers' page is the most-cited public reference; r/EmailMarketing has cohort-by-cohort testing threads where senders share the specific changes that moved subject lines from spam to inbox. The Word to the Wise blog has long-form posts on the content-classifier shift from rule-based to learned, which is the underlying change.
How to monitor Braze deliverability weekly
Four dashboards, 10 minutes a week, on the same day of the week so you compare like for like. (1) Braze Email Performance: send volume, delivery rate, complaint rate, unsubscribe rate, by campaign and by Canvas. (2) Google Postmaster Tools: spam rate, IP reputation, domain reputation, authentication results, all on a 24-hour delay. (3) Microsoft SNDS (Smart Network Data Services): complaint rate and trap-hit data per IP for Outlook and Hotmail. (4) Sender Score by Validity (free at senderscore.org): aggregated reputation 0 to 100 across multiple receiver signals. If any one of these moves more than 10 percent week-over-week, dig in the same day; deliverability degrades faster than it recovers, and a one-week lag in noticing turns a fixable issue into a four-week recovery. Most teams check these monthly; we check them weekly at clients because the cost of a missed signal is multiples of the time to look.
Further reading
Real, named sources the editor can swap in for specific URLs. We do not auto-link these because the right link changes over time. If you find a great primary source, write us and we will update the note.
- docs.braze.com: Email setup, IP warm-up, hard bounce management. Braze's canonical deliverability documentation. The three pages every email team should know cold.
- M3AAWG (Messaging Anti-Abuse Working Group) sender best practices. The industry-standard reference for ethical and effective sending. Free PDF; updated every two years.
- IAB Email Council guidelines. The buyer-side counterpart to M3AAWG. Useful for working with brand teams and legal.
- Google Postmaster Tools. Free Gmail-specific deliverability dashboard. The single most useful tool for any sender hitting Gmail at scale.
- Microsoft SNDS (Smart Network Data Services). Hotmail/Outlook equivalent of Postmaster Tools. Less polished but essential for Outlook-heavy lists.
- Sender Score by Validity (senderscore.org). Aggregated reputation score 0-100. Tracks all major receiver feedback in one number.
- r/EmailMarketing, r/EmailDeliverability, r/Braze. Working practitioner threads on complaint rate, IP reputation recovery, and Braze-specific deliverability patterns.
- WordToTheWise blog (Laura Atkins). The most-cited independent deliverability writer in the industry. Decades of working-source material.
Comments