Email Deliverability for Affiliates 2025 – Stats, Authentication & Best Practices

Email marketing continues to be one of the most profitable channels for affiliate programmes, yet success hinges on one crucial factor: deliverability. Your beautifully crafted newsletters and high‑converting CTAs are worthless if they end up in spam or never reach subscribers. A 2024 study across 15 leading email service providers (ESPs) measured an average deliverability rate of just 83.1 % meaning roughly one in five emails never hits the inbox. Poor deliverability doesn’t just depress open and click rates; it erodes trust and damages domain reputation. High bounce rates, spam complaints and disengaged lists signal to inbox providers that your messages don’t belong, so they filter aggressively.

This guide explains what email deliverability is, why it’s mission‑critical for affiliates, and how to achieve top‑tier inbox placement in 2025. We’ll break down key metrics (deliverability rate, bounce, spam complaint and sender reputation), explain authentication protocols (SPF, DKIM, DMARC, BIMI), and share proven tactics for list hygiene, segmentation, content optimisation and sending practices. By the end you’ll have a step‑by‑step blueprint to boost deliverability, recover lost revenue and build long‑term engagement with your audience.

Check our GA4 server-side tracking guide for insights on server-side analytics, and explore Omnisend’s deliverability study for more benchmarks.

1. Email Deliverability Affiliates 2025 – Definitions & Current Rates

Email deliverability refers to the percentage of messages that land in recipients’ inboxes rather than bouncing or being filtered as spam. It’s distinct from “delivery rate” (the ratio of emails accepted by a mail server) because it measures final inbox placement. The average deliverability across 15 ESPs in 2024 was 83.1 %. Anything bew 85 % signals problems: soft bounces (full mailbox or temporary failure), hard bounces (invalid addresses), spam‑filtering and low engagement scores. Gmail, Outlook and iOS Mail now use machine learning to score sender reputation; if your complaint rate exceeds 0.1 % or bounce rate rises above 2 %, future campaigns will be throttled or rejected.

1.1 Key Metrics & Benchmarks

• Deliverability rate: Share of sent emails that reach the inbox. Target ≥ 90 %.
• Hard bounce rate: Permanent failures (invalid domain, unknown user). Keep < 2 %.
• Soft bounce rate: Temporary issues (full inbox, busy server). Monitor trends—persistent soft bounces should be suppressed.
• Spam complaint rate: Percentage of recipients marking a message as spam; must stay < 0.1 %.
• Sender reputation: Composite score inbox providers assign based on engagement, complaints, bounces and spam traps. High reputation opens the door to inboxes.

Affiliates often face deliverability challenges because promotions and incentives can trigger spam filters. Aggressive cadence, poor segmentation and outdated lists lead to high unsubscribe and complaint rates. The next sections provide a framework to overcome these hurdles.

2. Set the Foundation: Authentication & Infrastructure

Before tweaking content or cadence, ensure your technical foundation is solid. Inbox providers verify that messages come from who they claim by checking authentication records. Without proper setup, your emails will be flagged as spoofing attempts and routed to spam.

• SPF (Sender Policy Framework): A DNS TXT record listing authorised IP addresses allowed to send mail on behalf of your domain. Implement a strict -all policy to prevent spoofers.
• DKIM (DomainKeys Identified Mail): Cryptographic signature that confirms the message hasn’t been altered and that it originates from your domain.
• DMARC (Domain‑based Message Authentication, Reporting & Conformance): Builds on SPF and DKIM; instructs inbox providers how to handle unauthenticated messages and sends you forensic reports. Start with p=none to monitor, then move to p=quarantine or p=reject.
• BIMI (Brand Indicators for Message Identification): Newer standard that displays your logo next to authenticated emails. Requires DMARC enforcement and a Verified Mark Certificate. Besides boosting recognition, BIMI acts as a trust signal to recipients.

to generate the required TXT records. Authentication is mandatory for deliverability: inboxes automatically down‑rank unsigned messages.

3. List Hygiene – Keep Your Data Clean

A bloated, outdated or purchased list is the fastest way to destroy deliverability. According to best‑practice guidelines, you must maintain a clean email list by confirming subscribers and pruning inactive addresses. Key steps:

1. Double opt‑in: Use a confirmation email when people sign up. This reduces fake or mistyped addresses and increases engagement.
2. Regularly remove hard bounces: Immediately suppress addresses that return a “user unknown” or “invalid domain” response.
3. Monitor soft bounces: If an address soft bounces for three consecutive sends, put it on a suppression list until you can verify.
4. Clean inactive subscribers: Periodically send re‑engagement campaigns. If a contact hasn’t opened or clicked in 90 days, move them to a dormant segment. Removing silent subscribers boosts your reputation; sending to them lowers your engagement rate.
5. Keep complaint rates low: Make your unsubscribe link prominent. It’s better for someone to opt out than to hit “Report spam.” Keeping complaint rates below 0.1 % is essential.

Segmentation further enhances deliverability because it aligns content with recipient expectations. Divide your list by vertical (casino, sportsbook, finance, health), lifecycle stage (new subscriber, active player, lapsed player) and engagement frequency. This allows you to deliver targeted offers rather than blasting everyone with the same promotion. Highly segmented campaigns consistently achieve higher open rates and lower spam complaints.

4. Crafting Messages That Land & Engage

Even with perfect authentication and a pristine list, poor content can still trigger spam filters or disengage readers. Follow these best practices:

• • Write compelling, clear subject lines: Avoid ALL CAPS, excessive punctuation and spammy phrases like “FREE,” “CLICK NOW” or “LOWER YOUR DEBT.” Personalised subjects (using the recipient’s first name or location) perform better.
  • Optimise preview text: Te snippet after your subject line should summarise the value; don’t repeat the subject or leave it blank.
  • Balance images and text: Use a healthy text‑to‑image ratio (around 60/40). Too many images can set off spam filters. Always include alt text and a plain‑text version.
  • Use responsive design: Over 60 % of affiliate emails are opened on mobile. Use a single‑column layout and large buttons; test across devices.

Configure these records at your DNS host. Use DMARC aggregate reports to spot spoofing attempts and misconfigurations. Many ESPs provide wizards lo

• Avoid large attachments: Instead of attaching PDF guides or coupons, link to a hosted file or landing page.
• Use a consistent sender name and “From” address: Changing sender names (e.g., “Support,” “Deals Team,” “No‑Reply”) confuses recipients and can reduce trust.
• Never send from a no‑reply address: It suppresses engagement signals (replies) and signals low customer care.

Also include a clear physical address and unsubscribe link to comply with CAN‑SPAM. Use short paragraphs, bullet points and whitespace to improve readability. When promoting affiliate offers, follow FTC guidelines: disclose affiliate relationships clearly and label ads. Transparent content maintains trust with subscribers and regulators.

5. Timing & Cadence – Warm Up and Maintain Your Sender Reputation

How and when you send emails influences deliverability as much as content. ISP algorithms monitor your sending patterns; erratic spikes look suspicious and can trigger throttling. Adopt the following best practices:

• Warm up new domains: If you’re using a fresh sending domain, ramp up volume gradually over several weeks. Start with small segments and gradually add more recipients. Sudden surges from a new domain are red flags.
• Establish a consistent cadence: Send at regular intervals (e.g., weekly or bi‑weekly). Inconsistency confuses filters and can harm reputation.
• Optimise send times: Test when your audience is most engaged. For many verticals, mid‑week mornings work well. Use time‑zone sending to deliver at local times.
• Monitor deliverability dashboards: Tools like GlockApps, Mailgun, SendGrid and Postmark provide real‑time feedback on inbox placement, bounce categories and spam trap hits. Use these insights to adjust quickly.
• Avoid “blast all” campaigns: Use behavioural triggers (e.g., sign‑up confirmation, deposit reminder, VIP reward) to send timely, relevant messages. Triggered emails typically achieve 70 % higher open rates and 50 % lower unsubscribe rates.

If you notice deliverability dropping, slow down your sends and focus on re‑engaging your most active subscribers. Conduct A/B tests on subject lines, from names and sending times to identify what resonates with your list. Always keep an eye on bounce and complaint metrics and adjust your suppression rules accordingly.

6. Tools to Monitor & Improve Deliverability

Modern deliverability isn’t guesswork; it relies on diagnostic tools. Consider integrating these solutions into your workflow:

Most major ESPs (Mailchimp, ConvertKit, ActiveCampaign, Braze) now include built‑in deliverability dashboards and domain‑warming tools. Use them to monitor your key metrics after every send and adjust accordingly. Don’t forget to check your DNS records periodically; sometimes third‑party mail services update IPs and you must update SPF accordingly.

7. Ten‑Step Action Plan to Boost Deliverability

1. Set up SPF, DKIM, DMARC and BIMI on your sending domain.
2. Warm up new domains gradually; start with your most engaged segment.
3. Implement double opt‑in and remove hard bounces immediately.
4. Regularly clean inactive subscribers and monitor bounce/complaint rates (<2 % and <0.1 %).
5. Segment your list by vertical, lifecycle stage and engagement.
6. Craft concise, personalised subject lines and avoid spam triggers.
7. Design responsive, accessible emails with a balanced text‑to‑image ratio.
8. Use behavioural triggers instead of “blast all” campaigns.
9. Test send times and adjust cadence based on engagement signals.
10. Leverage deliverability tools (GlockApps, Mailgun, SendForensics) and monitor your reports after every send.

Implementing all of these steps will dramatically improve your chances of reaching the inbox. More importantly, they create a virtuous cycle: better deliverability → higher opens & clicks → improved sender reputation → even better deliverability.

8. Takeaway – Email Deliverability Affiliates 2025

Deliverability is the heartbeat of affiliate email marketing. While 83.1 % average inbox placement suggests there’s still a long way to go, affiliates who prioritise authentication, list hygiene, segmentation and compelling content can reach the elusive 95 %+ tier. Treat deliverability as a continuous process rather than a one‑time setup; monitor your metrics, refine your messaging and respect your subscribers’ preferences. Do this, and your newsletters will consistently land where they belong: front and centre in your readers’ inboxes.

Sources

1. Omnisend deliverability guide summarising a 2024 EmailTooltester study: average deliverability across 15 ESPs was 83.1 %; poor deliverability erodes trust and domain reputation.
2. Omnisend best practices: emphasise SPF/DKIM/DMARC/BIMI authentication, cleaning lists, keeping bounce rate <2 % and complaint rate <0.1 %, double opt‑in, segmentation and responsive design.
3. Omnisend advanced deliverability tips: segment inactive subscribers, personalise content, avoid no‑reply senders, test send times and warm up domains gradually.