How to Improve Email Deliverability: The Complete 2026 Guide

What Is Email Deliverability?

Email deliverability is the ability of your email to successfully reach a subscriber's inbox - rather than being filtered into spam, promotions, or blocked entirely.

A 95% deliverability rate doesn't mean 95% of emails go to the inbox. It means 95% were accepted by the receiving mail server - some of those may still land in spam. The metric that actually matters is inbox placement rate: the percentage of delivered emails that land in the primary inbox.

The average inbox placement rate across all email senders is around 85%. The best senders - with clean lists, proper authentication, and great content - achieve 98%+. Mailsend.dev customers average 98.7%.

Step 1: Set Up SPF, DKIM, and DMARC

Domain authentication is the foundation of email deliverability. Without it, even high-quality emails get filtered as suspicious. You need to configure three DNS records:

SPF (Sender Policy Framework)

SPF tells receiving mail servers which IP addresses are authorized to send email on behalf of your domain. Add an SPF record to your DNS that includes your email service provider's IP ranges.

DKIM (DomainKeys Identified Mail)

DKIM adds a cryptographic signature to your emails that receiving servers can verify. This proves the email was actually sent by your domain and wasn't tampered with in transit.

In Mailsend, DKIM setup is automatic - we generate the key pair and you add the public key as a DNS TXT record. It takes about 2 minutes.

DMARC (Domain-based Message Authentication)

DMARC is a policy that tells receiving servers what to do when SPF or DKIM checks fail - quarantine the email, reject it, or take no action. Start with a monitor-only policy:

Once you've confirmed your legitimate email passes authentication (monitor for 2-4 weeks), move to p=quarantine and eventually p=reject.

Step 2: Warm Up Your Sending Domain

If you're new to sending email from a domain - or restarting after a period of inactivity - you need to warm up your sending reputation. ISPs like Gmail and Outlook track sending patterns and are suspicious of new domains that suddenly send thousands of emails.

Domain warming is the process of gradually increasing your sending volume over 2-4 weeks, starting with your most engaged subscribers and slowly expanding to your full list. This builds a positive reputation before you hit high volumes.

Mailsend includes a built-in domain warm-up tool that automates this schedule for you. Learn more about Mailsend's deliverability tools →

Step 3: Clean Your Email List

An unclean list is the #1 cause of deliverability problems for established senders. Over time, email addresses become invalid, people abandon inboxes, and spam traps are seeded into purchased lists.

Signs your list needs cleaning:

• → Hard bounce rate above 2%
• → Open rate declining month-over-month
• → Spam complaint rate above 0.1%
• → Sudden drop in open rate
• → ISP feedback loop complaints increasing

How to clean your list: Remove hard bounces immediately. Run a re-engagement campaign to identify active subscribers, then suppress anyone who hasn't opened in 6+ months. Validate email addresses on import using an email verification tool.

Step 4: Monitor Your Sender Reputation

Your sender reputation is a score that ISPs assign to your IP address and domain based on your sending history. A poor reputation means your emails get filtered, regardless of content quality.

Key metrics to monitor:

• → IP reputation score (check via Google Postmaster Tools)
• → Domain reputation (Google Postmaster Tools → Domain section)
• → Blacklist status (Spamhaus, Barracuda, SURBL)
• → Spam complaint rate (target: below 0.1%)
• → Gmail inbox placement rate vs. spam rate

Mailsend monitors your reputation across all major blacklists in real-time and alerts you immediately if any issues are detected. See reputation monitoring →

Step 5: Manage Bounces and Complaints

Hard bounces (invalid email addresses) must be removed from your list immediately. Continuing to send to them signals poor list hygiene to ISPs and damages your reputation.

Mailsend handles this automatically - hard bounces are permanently suppressed after the first occurrence. Soft bounces (temporary failures like a full inbox) are retried 3 times before suppression.

For spam complaints: every complaint counts against you. Mailsend is enrolled in Gmail, Yahoo, and Outlook feedback loops - the moment a subscriber marks your email as spam, they're automatically suppressed to prevent future complaints.

Step 6: Write Emails That Don't Trigger Spam Filters

Modern spam filters (especially Gmail's) are more sophisticated than keyword matching. They evaluate the full context of your email - authentication, sender reputation, subscriber engagement, and content signals.

Content best practices for deliverability:

• → Maintain a healthy text-to-image ratio (avoid image-only emails)
• → Avoid spam trigger words in subject lines (FREE, URGENT, ACT NOW)
• → Never use URL shorteners (bit.ly, t.co) - they're frequently blacklisted
• → Use a consistent From name and From address subscribers recognize
• → Include a plain text version of every HTML email
• → Keep your unsubscribe link prominent and one-click accessible

Step 7: Use a Dedicated IP Address

A dedicated IP address means only your domain uses that IP for sending. This isolates your sender reputation - you're not affected by other senders' poor behavior.

Shared IPs (used by most entry-tier email platforms) pool multiple customers together. If another sender on your shared IP has a high complaint rate, it can affect your inbox placement.

Dedicated IPs are recommended for senders sending 100,000+ emails per month. They require a warm-up period but provide much tighter control over your reputation long-term.

Email Deliverability Checklist