Your Klaviyo open rates do not mean what you think they mean if your emails are landing in spam. 15 to 20 percent of commercial emails never reach the inbox across major providers. For D2C brands with 50,000 subscribers, that is 7,500 to 10,000 people per send who never see your email. Deliverability is not a technical footnote. It is a revenue multiplier.
The Three Pillars of Email Deliverability
Authentication: DNS records that prove to email providers that your sending domain is legitimate. SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication) must all be correctly configured. Klaviyo provides the specific DNS records you need to add to your domain. Without these, your emails look like spam to filters regardless of content quality. Authentication is non-negotiable and takes 30 minutes to set up correctly.
Sender reputation: Email providers maintain a reputation score for every sending IP address and domain. High spam complaint rates, high bounce rates, and low engagement rates all damage reputation. A damaged sender reputation causes all emails from your domain to be filtered, not just the problematic ones. Reputation builds slowly with good sending practices and can be destroyed quickly with one badly managed campaign to an unclean list.
List quality: Who is on your list matters as much as how you send. A list full of unengaged subscribers, role addresses (info@, sales@, admin@), and invalid emails hurts your reputation. Clean your list quarterly. Suppress anyone who has not opened or clicked an email in 180 days before a major campaign.
Spam Complaint Rate: The Number That Kills Programmes
Spam complaint rate is the percentage of recipients who mark your email as spam. Google's threshold: above 0.3 percent spam complaint rate causes significant inbox placement problems. Above 0.1 percent consistently warrants investigation. Industry average is below 0.05 percent for well-managed programmes.
What causes high spam complaints: sending to people who did not explicitly opt in, sending too frequently to an unengaged list, subject lines that feel misleading or bait-and-switch, and not having a clear and easy one-click unsubscribe option. Klaviyo's one-click unsubscribe is enabled by default. Never disable it. An unsubscribe is infinitely less damaging than a spam complaint.
List Hygiene Process
Quarterly list audit: In Klaviyo, create a segment of subscribers who have not opened any email in the last 180 days. This is your suppression candidate list. Do not immediately suppress. Run a re-engagement campaign first: 2 to 3 emails over 2 weeks with genuinely compelling content or an offer. Suppress anyone who does not engage with the re-engagement campaign.
Bounce management: Hard bounces (invalid email addresses) should be automatically suppressed after one bounce. Klaviyo does this automatically. Review your bounce report monthly. Bounce rates above 2 percent indicate a list quality problem at the source, typically a pop-up form that allows invalid email entry. Add email validation to your opt-in forms.
Warm-Up Protocol for New Sending Domains
If you are launching a new email programme or switching to a custom sending domain, you must warm up the domain gradually. Starting with 10,000 sends on day one to a cold domain will result in filtering by every major email provider. Week 1: send to your most engaged subscribers (opened in last 30 days), 500 to 1,000 per day. Week 2: expand to 30-day openers, 2,000 to 3,000 per day. Week 3: expand to 90-day openers, 5,000 to 10,000 per day. Week 4 and beyond: expand to full list incrementally. This 4-week warm-up establishes domain reputation before high-volume sending.