How to Improve Email Deliverability in 2025

Published on November 6, 2025 • by MailTested Team

You’ve built your list, written a great email, hit “Send” — and it vanishes into spam. That’s not bad luck, it’s bad deliverability. In 2025, mailbox providers have raised the bar on authentication, engagement, and content trust. If your domain, infrastructure, or reputation isn’t airtight, your messages won’t even reach the inbox.

This guide breaks down the critical technical and behavioral fixes that actually improve email deliverability — based on thousands of domain tests from MailTested.

1️⃣ Authenticate Your Domain — SPF, DKIM, and DMARC

Email deliverability starts with authentication. Without valid SPF, DKIM, and DMARC records, mailbox providers like Gmail and Outlook simply can’t verify you. Unauthenticated mail is treated as a phishing risk — no matter how legitimate your business is.

Here’s what each record does:

• SPF tells the world which mail servers can send for your domain.
• DKIM uses cryptographic signatures to confirm your messages aren’t altered.
• DMARC enforces that both SPF and DKIM align, providing full identity assurance.

If any of these fail, your email will pass through fewer filters and often land in spam. Use MailTested’s SPF, DKIM, and DMARC checks to verify whether your setup is passing authentication.

2. Protect and Build Your Sender Reputation

Think of your sender reputation as your “email credit score.” It’s determined by how people interact with your messages — opens, clicks, replies, and complaints. When your reputation dips, your inbox placement drops.

Common factors that damage reputation:

• Frequent hard bounces from old or fake emails
• Low engagement rates or mass unsubscriptions
• Spam complaints above 0.1%
• Sudden spikes in sending volume

The fix: keep your lists clean, verify addresses before sending, and warm up new IPs gradually.

3. Fix Content That Triggers Spam Filters

Even with perfect DNS authentication, bad content can kill deliverability. Mailbox filters analyze wording, layout, and even HTML structure to detect spam patterns. Avoid shouty subject lines, unnecessary capitalization, and heavy use of images or links.

Best practices for 2025:

• Keep your subject line under 60 characters, no clickbait
• Use a clean “From” name (match domain and brand)
• Balance text-to-image ratio — never image-only emails
• Include an unsubscribe link and physical address

You can test your content’s spam score by sending it to MailTested — it simulates how major filters will treat your message before you send it.

4. Keep a Consistent Sending Pattern

Inconsistent volume is one of the biggest signals mailbox providers use to flag spam behavior. Sending 50 emails one day and 10,000 the next looks like bot activity — even if you’re legit.

If you’re launching a new domain or IP, ramp up gradually:

Day 1–3: 100 emails/day  
Day 4–7: 500 emails/day  
Week 2: 1,000–2,000 emails/day  
After Week 3: Scale slowly to target volume

The goal is to train spam filters that your traffic is predictable and reliable. MailTested can help track engagement across test sends so you spot warning signs early.

5. Monitor Blacklists and DNS Health

Even if you’ve done everything right, a single listing on a public blacklist (Spamhaus, Barracuda, UCEPROTECT) can block your messages entirely. Check your IP and domain regularly — reputation decays silently over time.

If you find a listing, remove the root cause first — spam complaints, compromised accounts, or shared IP abuse — before requesting delisting.

6. Use Feedback Loops and Engagement Signals

Mailbox providers constantly adjust deliverability based on engagement signals — opens, clicks, and replies. When users interact positively, your reputation improves; when they ignore or mark as spam, it sinks.

Actionable engagement steps:

• Segment inactive users and re-engage or remove them
• Encourage replies to transactional and onboarding messages
• Send personalized content to maintain relevance

7. Test, Track, and Tune

Email deliverability isn’t a one-time fix — it’s an ongoing cycle of testing and adjustment. Every time you change a mail provider, IP, or DNS record, re-run deliverability tests.

MailTested provides full scoring for SPF, DKIM, DMARC, spam filters, and IP reputation — helping you maintain a clean sender identity and top-tier inbox rate.

✅ Final Thoughts

Improving deliverability means mastering three pillars: authentication, reputation, and relevance. When you consistently pass authentication, maintain a solid IP score, and send valuable content, your inbox placement improves naturally — no hacks, no gimmicks.

MailTested gives you the full picture — authentication status, content score, and provider-specific feedback — so you can fix weak spots before they cost you deliverability.