Klaviyo is the dominant email marketing platform for direct-to-consumer e-commerce — particularly Shopify and WooCommerce merchants — and its integration depth with those platforms is genuinely impressive. What is less impressive is how many Klaviyo accounts I see operating with default authentication settings, shared IP pools, no suppression strategy, and flow configurations that are quietly destroying sender reputation through systematically low-engagement sends. Klaviyo makes it very easy to start sending; it requires deliberate configuration to send well.
This guide is for Klaviyo users who have outgrown the default setup — either because deliverability is already a problem, or because they want to build the infrastructure foundation that prevents it from becoming one. I am not going to cover the basics of setting up a Klaviyo account or creating a campaign. I am going to cover the deliverability-specific configuration decisions that have real impact on inbox placement and sender reputation.
Shared vs Dedicated IPs in Klaviyo: When to Make the Move
Most Klaviyo accounts send from Klaviyo's shared IP pools. The shared pools are maintained by Klaviyo's deliverability team and generally perform well for accounts with good list hygiene and engagement practices — Klaviyo actively monitors and removes senders from shared pools who generate complaint rates above threshold, which protects the pool's reputation for compliant senders. For the majority of Klaviyo users, shared IPs are the right configuration: they benefit from pool-level reputation management without the overhead of dedicated IP warmup and maintenance.
The threshold at which dedicated IPs become appropriate: generally around 500,000-1,000,000 emails per month sent with consistent frequency. Below this volume, dedicated IPs often hurt deliverability rather than helping — a dedicated IP requires enough volume to maintain its own sending reputation signal, and a low-volume sender on a dedicated IP has less reputation history than the same sender would have on Klaviyo's well-maintained shared pool. Above this volume, dedicated IPs provide the reputation isolation that protects high-performing programmes from being affected by other senders' events on the shared pool.
Klaviyo's dedicated IP option requires working with their deliverability team and costs additional fee on top of the standard plan. Before requesting dedicated IPs, ensure: (1) custom subdomain authentication is fully configured; (2) list hygiene is active (60-day sunset policy minimum); (3) your sending frequency is consistent enough to maintain dedicated IP reputation (at least 3-4 major sends per month, not 1-2 seasonal campaigns). A dedicated IP that sits idle for 6 weeks between campaigns loses its reputation and the next send goes to spam — the consistent sending requirement for dedicated IPs is a genuine operational constraint, not a suggestion.
Subdomain Authentication: The Non-Negotiable First Step
By default, Klaviyo sends email using Klaviyo's own domain alignment — DKIM signed with klaviyomail.com, SPF passing for Klaviyo's infrastructure. This works functionally but means your email is authenticated as Klaviyo's infrastructure rather than your brand's domain. The business and deliverability consequences:
(1) Spam filter content analysis associates the email with klaviyomail.com reputation rather than your brand domain. If klaviyomail.com has any shared reputation events (from other Klaviyo users on the same infrastructure), your email inherits those effects. (2) DMARC aggregate reports for your domain will not include Klaviyo-sent email, because it is authenticated to klaviyomail.com rather than your domain — making it invisible in your DMARC monitoring. (3) Recipients with sophisticated spam filters may see "From: Brand Name but actually sent via klaviyomail.com" disclosures that undermine trust in the sender identity.
The fix is custom subdomain authentication: configuring a sending subdomain of your brand domain (email.yourbrand.com or sends.yourbrand.com) and publishing the DKIM and SPF DNS records that Klaviyo generates for that subdomain. After this configuration, Klaviyo signs your email with DKIM under your brand subdomain, and SPF authenticates from your subdomain — making the email fully DMARC-aligned to your brand domain rather than Klaviyo's.
# Klaviyo custom subdomain DNS setup: # Klaviyo generates specific DNS records for your subdomain # Access these at: Klaviyo → Settings → Email → Sending Domains # Example records Klaviyo will ask you to publish (specific values vary): # CNAME for email tracking subdomain: tracking.yourbrand.com CNAME tracking.klaviyo.com # DKIM records (Klaviyo generates both, publish both): kl1._domainkey.email.yourbrand.com CNAME kl1.dkim.klaviyomail.com kl2._domainkey.email.yourbrand.com CNAME kl2.dkim.klaviyomail.com # SPF record for your sending subdomain: email.yourbrand.com TXT "v=spf1 include:klaviyomail.com ~all" # DMARC for your root domain (if not already configured): _dmarc.yourbrand.com TXT "v=DMARC1; p=quarantine; rua=mailto:dmarc@yourbrand.com" # Verify after 24-48 hours: # dig CNAME kl1._domainkey.email.yourbrand.com # dig TXT email.yourbrand.com # Klaviyo's Settings panel shows verification status for each record # From: address should use the custom subdomain: # from: Brand Name <hello@email.yourbrand.com> # NOT: from: Brand Name <hello@yourbrand.com> # (root domain from address creates alignment complexity unless # DKIM or SPF also aligns to root domain — subdomain is cleaner)
Klaviyo IP Warm-up: What the Platform Does and What You Must Do
When you configure custom subdomain authentication in Klaviyo, you are effectively introducing a new sending subdomain to ISPs — one with no reputation history. Klaviyo routes the initial traffic through their shared IP pools for the new subdomain, gradually building domain reputation before transitioning to your dedicated IPs (if applicable). The platform handles some of this automatically, but there are critical things it does not do that you must handle manually.
What Klaviyo handles automatically: Volume throttling during the initial weeks after subdomain setup (Klaviyo limits how much email can go through the new subdomain to prevent volume spikes that damage new domain reputation); basic deliverability monitoring on their end to detect unusual patterns; technical DKIM and SPF alignment for your configured subdomain.
What you must handle: Recipient selection during warmup is your responsibility, not Klaviyo's. Klaviyo will send to whatever segments or lists you configure in your campaigns and flows, including lapsed subscribers who should be excluded during warmup. The correct approach: for the first 30-60 days after activating custom subdomain authentication, restrict campaigns to a "Highly Engaged" segment — recipients who have opened or clicked within the last 30 days. This sends your new subdomain's initial reputation-building email to the audience most likely to engage positively, rather than to your entire list including lapsed contacts who are complaint risks. After 30-60 days of consistently good engagement from the highly engaged segment, gradually expand the sending audience. Only bring the full list to the new subdomain after it has established Good domain reputation at Gmail Postmaster Tools (which you should register for the new subdomain immediately).
Suppression Management in Klaviyo: Lists, Segments, Suppressions
Klaviyo has three distinct suppression mechanisms, and understanding how they interact is critical for maintaining good deliverability:
Klaviyo's automatic suppressions: Hard bounces, spam complaints (via Klaviyo's FBL integration), and manual unsubscribes are automatically suppressed by Klaviyo. These are permanent suppressions — they apply across all lists and cannot be overridden by re-adding the contact. This is the correct behaviour: a hard-bouncing address should never receive email again regardless of which list it is on.
Manual suppression list: Klaviyo allows uploading a custom suppression list (Settings → Suppressions → Upload) for addresses you want to exclude from all sends — for example, emails from competitors, known spam trap domains you have discovered, or contacts who have requested suppression through channels other than the standard unsubscribe link. This list applies globally across all sends.
Segment-based exclusion (sunset policy): This is where most Klaviyo accounts have gaps. Klaviyo does not automatically suppress unengaged contacts — it sends to them indefinitely unless you configure your campaigns and flows to exclude them. The standard approach is to create a "Sunset" segment (contacts who have not opened or clicked any email in 180 days) and exclude this segment from all campaign sends. This requires:
# Klaviyo Sunset Segment definition (create in Lists & Segments):
Conditions:
- Properties about someone → Last Opened Email → over 180 days ago
OR
- Properties about someone → Last Clicked Email → over 180 days ago
(whichever is more recent)
AND
- Email → is not suppressed
# Campaign configuration to exclude sunset contacts:
# When creating a campaign:
# Recipient: → Include [your main list]
# Exclude: → [Sunset Segment] ← This is what most people skip
# Result: campaigns only send to contacts who have engaged in 180 days
# The lapsed 180+ days contacts accumulate in the sunset segment
# where they should receive only a re-engagement campaign
# before being removed entirely
# The hard truth about Klaviyo deliverability:
# An account with 100,000 profiles but 60,000 in the sunset segment
# that sends to all 100,000 is operating at roughly 25% effective
# engagement rate — which looks like 25% open rate in analytics
# but is actually closer to 65%+ among the genuinely engaged 40,000
# The other 60,000 are dragging domain reputation down daily
Flow-Specific Deliverability: Win-Backs, Abandonment, and Post-Purchase
Klaviyo flows — automated email sequences triggered by specific events — create the most difficult deliverability problems to diagnose because they run continuously in the background without the explicit review that campaign sends receive. A flow configured 18 months ago may be silently generating complaint spikes from edge cases that nobody anticipated when the flow was designed.
Win-back flows (the most dangerous): Win-back flows targeting unengaged contacts are by definition sending to people who have not responded to prior email. The longer the win-back flow extends — some I have seen continue for 12-18 months of inactivity — the more it reaches contacts who are either no longer interested, have forgotten the brand, or have changed email addresses to the point where their former address is generating soft bounces. The deliverability discipline for win-back flows: cap them at 90-120 days of inactivity maximum. Anyone inactive beyond 120 days who does not respond to the win-back sequence is suppressed. Continuing win-back attempts beyond 120 days generates diminishing returns in win-back rate and increasing complaint risk from frustrated recipients who have definitively moved on.
Abandoned cart and browse abandonment flows: These are typically high-engagement flows with low complaint rates — the recipient was actively considering the product and is receiving a contextually relevant follow-up. The deliverability risk is in the flow configuration: how many emails, how long after abandonment. A 3-email abandoned cart sequence over 24 hours is appropriate. An 8-email sequence over 14 days becomes persistence that recipients eventually mark as spam. Audit flow lengths against industry benchmarks: 2-3 emails for abandoned cart (24 hours to 72 hours after abandonment), 1-2 emails for browse abandonment (4-8 hours after browse).
Post-purchase flows: Post-purchase flows — confirmation, shipping notification, delivery, review request, cross-sell — are generally high-engagement because the recipient has just transacted. The deliverability risk comes from the cross-sell component: sending 5 cross-sell emails after every purchase to a customer who bought once and has no intention of buying again generates complaint rates that accumulate over time. Cap cross-sell emails at 2-3 per purchase cycle; gate subsequent cross-sell on demonstrated engagement (opened previous cross-sell emails).
Campaign Sending Strategy: Segments, Timing, and Frequency Caps
Campaign deliverability in Klaviyo is determined by who you send to, when you send, and how often — and the interactions between these three variables.
Segment selection as the primary deliverability lever: The single most impactful campaign deliverability action is recipient segmentation that excludes low-engagement contacts. The "Highly Engaged" segment (opened or clicked in last 30 days) generates the best engagement rates and lowest complaint rates. The "Active" segment (opened or clicked in last 90 days) is a reasonable production-sending segment with good deliverability outcomes. The full list (all subscribers including 180+ day inactive) produces the worst deliverability outcomes and should only be used for re-engagement campaigns specifically designed for that audience, not for regular promotional sends.
Timing and ISP capacity: Klaviyo's send time optimisation feature (Smart Send Time) uses historical engagement data to predict when each subscriber is most likely to open email. This feature is valuable for engagement rate improvement but has a deliverability nuance: Smart Send Time concentrates sends at specific times that the model predicts are optimal, which can create volume spikes at Gmail and Yahoo as many recipients receive email at the same algorithmically determined "best time." For very large lists (500k+), consider whether Smart Send Time creates volume concentration that approaches ISP rate limit thresholds — if so, a time window send (e.g., "send between 8am and 10am local time") distributes volume more smoothly than Smart Send Time's point-in-time concentration.
Frequency caps: Klaviyo allows frequency caps in flows (minimum time between messages) but does not natively enforce frequency caps across all sends combined — a subscriber can receive both a campaign email and a flow email on the same day, and another campaign the next day. This cumulative frequency is invisible in standard Klaviyo analytics but visible in complaint rate. Implement a frequency exclusion segment: exclude any contact who has received an email within the last N days (where N depends on your programme's standard frequency). This prevents the contact who received a win-back email on Monday from also receiving a promotional campaign on Tuesday — a combination that generates complaints from recipients who experience the cumulative volume as harassment.
Deliverability Monitoring Inside and Outside Klaviyo
Inside Klaviyo: Klaviyo's campaign analytics provide bounce rates, unsubscribe rates, spam complaint rates, and open/click rates. The metrics to monitor weekly: spam complaint rate (target below 0.05%, alert threshold above 0.08%); hard bounce rate per campaign (alert if above 0.5% — indicates list quality decay in the specific segment used); and open rate trend over time (declining open rate with stable list composition indicates deliverability degradation, not just engagement decline).
Klaviyo also provides a deliverability health tab in some account tiers that surfaces ISP-level delivery data. This is less detailed than Gmail Postmaster Tools but covers the basics — Gmail delivery rate, Microsoft delivery rate, Yahoo delivery rate — that can identify ISP-specific problems before they show in aggregate campaign analytics.
Outside Klaviyo — essential: Gmail Postmaster Tools for the custom sending subdomain (email.yourbrand.com or whatever subdomain you configured). Register immediately after configuring custom subdomain authentication. Review domain reputation chart weekly. The spam rate chart in Postmaster Tools is more accurate than Klaviyo's reported spam complaint rate for Gmail-domain recipients, because it includes spam folder placement that Gmail users did not actively mark but that Gmail's automated systems classified as spam.
The Klaviyo Settings Most Users Never Configure
Beyond authentication and suppression, these Klaviyo settings have material deliverability impact and are frequently left at defaults:
List-Unsubscribe header (Settings → Email → Sending): Klaviyo adds the List-Unsubscribe header by default — but verify this is active and configured to the correct reply-to address. The List-Unsubscribe-Post header (for one-click unsubscribe as required by Gmail and Yahoo for bulk senders) should also be verified. If Klaviyo's compliance settings show these headers are active, no action needed; if they are not, contact Klaviyo support — this is a MAGY compliance requirement that Klaviyo handles for you, but verify it is actually working.
Double opt-in (List settings → Double Opt-in): Double opt-in is off by default in Klaviyo. Enabling it sends a confirmation email to new subscribers before adding them to the list. Double opt-in produces a smaller list but a dramatically better-quality list — confirmation rates of 60-80% mean 20-40% of signups are either invalid email addresses or low-intent subscribers who don't complete confirmation. The list that results has lower hard bounce rates, lower complaint rates, and better engagement metrics. For programmes in CASL (Canada) or GDPR (EU) jurisdictions, double opt-in documentation is also valuable for compliance evidence.
Unsubscribe page customisation (Account → Settings → Email → Unsubscribe page): The default Klaviyo unsubscribe page offers "Unsubscribe from all" as the primary action. Customising this page to offer preference management (opt down to less frequent emails rather than full unsubscribe) reduces the number of complete unsubscribes from recipients who are not hostile but simply want less email. These preference-managed contacts convert at lower rates but are recoverable; fully unsubscribed contacts are not.
Klaviyo Deliverability Booster: Available in some Klaviyo tiers, this feature provides additional inbox placement testing and deliverability insights. If your account tier includes it, enable it — the additional seed list data for inbox placement by ISP is valuable for detecting delivery problems that standard campaign analytics miss.
Klaviyo is a capable platform that can support excellent email deliverability when configured correctly. The configurations that differentiate good-performing Klaviyo accounts from struggling ones are not technically complex — custom subdomain authentication, a sunset suppression segment, flow length caps, and Gmail Postmaster Tools monitoring cost roughly 4-8 hours to implement and provide ongoing deliverability benefits that compound over months and years of programme operation. The accounts that skip these configurations in favour of faster time-to-first-send consistently reach a ceiling on programme performance that the configuration investment would have prevented.