Deliverability starts with a solid foundation, including a valid shipping address and a well-configured domain (SPF, DKIM, DMARC) to prove your legitimacy. Beyond that, there are a number of practical, little-known tricks that can boost your inbox insertion rate. The use of personalization and segmentation is crucial: by targeting each group of recipients by their interests, behavior or level of engagement, your emails will be more relevant and generate more opens. Segmentation improves engagement and deliverability. For example, segment your lists by geographic origin, purchase history or past interactions to deliver content tailored to each profile. You can also integrate a preference center so that subscribers can self-segment (choosing frequency or content categories), thereby boosting their interest and reducing unsubscribes.
Content, timing and commitment
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- Object and content optimization : Keep email subject lines clear and short (ideally 35-50 characters). Avoid capitalized words, excessive exclamation marks and garish, spam-like colors. Eliminate "spammy" words (eg. Free, Urgent), as recommended by the deliverability guides. Choose a text/image ratio of around 70/30 to avoid falling foul of spam filters, and don't do not join always send large files (PDF, ZIP, etc.), as ISPs are wary of mass e-mails with attachments. An email that is too large (generally >100-200 Kb) also runs the risk of being truncated or considered suspicious.
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- Relevance and commitment : Send the content your subscribers expect. Don't rush promotions or news to those who haven't asked for it: the more content matches the recipient's expectations, the higher its open and click rate, which strengthens your reputation as a sender. Conduct A/B tests on your subject lines and content to maximize engagement (the number of opens and clicks) - this sends positive signals to ISPs about your emails. Pay particular attention to previews and mobile display: your campaigns should display correctly on all devices and inboxes. Finally, experiment with the best time to send (by time zone or recipient profile) so that your message doesn't arrive at the wrong time (for example, in the middle of the local night).
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- List cleaning and follow-up : Keep your contact list healthy by cleaning it on Snapshoot. Remove permanently bounced or unsubscribed addresses immediately, and consider removing contacts that have been inactive for several campaigns. SparkPost reminds you that spam traps (spam traps) used by ISPs detect poorly maintained lists: sending many e-mails to these dummy addresses often leads to them being blocked or classified as spam.
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- Key performance indicators (KPIs) : Regularly monitor your statistics: bounce rate, spam reports, opens, clicks and conversion rates. These KPIs enable you to quickly detect a deliverability problem. For example, a high complaint rate (even <0.1 % is enough to trigger an alert at Gmail) or a drop in open rate indicates that you need to adjust your frequency or segment your mail differently. A delivery rate close to 100 % doesn't mean everything (this rate simply measures the percentage of accepted mailings, including spam), it's rather the inbox insertion rate that counts to assess the impact of your optimizations.
Advanced technical recommendations
Beyond good marketing practices, the technical aspect is decisive in maximizing deliverability. Authentication and DNS : Make sure you have the correct DNS records. At the very least, configure SPF and DKIM, and publish a DMARC policy (p=quarantine or reject) with RUA/RUF addresses to receive reports. More advanced protocols such as BIMI (display of brand logo in Gmail), MTA-STS and TLS-RPT reinforce ISP confidence by guaranteeing TLS encryption of SMTP exchanges. For example, Google Postmaster requires emails to be sent using TLS and authenticated. Don't forget to align your domains: the From header should be consistent with authenticated domains, otherwise filters will consider it suspicious.
IP address management
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- Dedicated vs. shared IP : A dedicated IP belongs entirely to you: your reputation no longer depends on other senders. This is essential when you're sending large volumes. If you adopt a dedicated IP, take care with the warm-up: We recommend a gradual warm-up, e.g. ~300 emails the first day, then +20 % of volume each day. Consult an expert if you need to accelerate this plan. Avoid jerky sending: ideally, send every day at a regular volume to build a reliable reputation.
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- IP reputation and pools : Concentrate your mailings on the most engaged recipients during the warm-up period to maintain a low complaint rate. Once launched, segment your mailings by IP "pools" (by product line, geographic area, etc.) to isolate the impact of each campaign on reputation. Monitor IP reputation with third-party services (Sender Score, Talos, Google Postmaster).
Monitoring and specialized tools
Use the Postmaster tools available: Google Postmaster Tools (for Gmail) provides metrics on domain/IP reputation, reported spam and delivery errors. Microsoft offers SNDS (Smart Network Data Services) for Outlook/Hotmail. Keep an eye on User-Reported Spam Rate Gmail recommends staying well below 0.1 %.
Also consider seed-testing solutions: send your e-mails to lists of dummy mailboxes at different ISPs (services such as GlockApps), Mail-tester) to check your inbox placement, spamming or blocking. Similarly, DMARC aggregate (RUA) and forensic (RUF) reports tell you whether certain ISPs are rejecting or classifying your messages as fraudulent.
Technical structure of the message
Email format influences deliverability. Standard headers : include a header List-Unsubscribe compliant (e.g. a one-click unsubscribe link according to RFC8058 to facilitate unsubscribing and satisfy Gmail requirements. Use clean MIME encoding: for examplequoted-printable encoding for the HTML body, to avoid spam filters that hate massive base64-encoded mailings. Make sure that the URLs included don't redirect too much, and that they point to trusted domains (avoid shortened links or links to unknown sites).
Write semantically correct, lightweight HTML: poorly formed or overly complex code can trigger filters. Avoid misleading or hidden content (e.g. text hidden by color). Finally, keep an eye on your complaint rate Every user complaint damages your reputation. Use the feedback loops (ARF reports) offered by some suppliers to understand and deal with complaints.
Conclusion
By applying these marketing and technical tips, respecting the rules of the CNIL and by keeping a close eye on your indicators (open rates, bounces, spam reports, reputation), you significantly maximize the probability that your emails will reach the right place. Be ready to adjust your strategy on an ongoing basis: deliverability is a balance between the art of the message and the science of protocols.
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