You spent an hour crafting the perfect email campaign. You hit send. And then… nothing. Half your list never sees it because their email provider decided your message looks like spam and filtered it out before it ever reached their inbox.
Email deliverability — the ability to actually land in recipient inboxes — is one of the most misunderstood aspects of email marketing. You can have the best offer, the most compelling copy, and beautiful design, but none of it matters if your emails never get delivered.
Understanding How Email Filtering Works
Every major email provider uses sophisticated algorithms to decide which messages reach the inbox and which go to spam. These systems analyze hundreds of factors including your sender reputation based on past behavior, your email authentication records, the content and structure of your message, how recipients have interacted with your previous emails, and whether you are sending from a known spam source.
Think of deliverability like a credit score for email senders. Every action you take affects your reputation. Send high-quality emails that people engage with and your score improves. Send spam or low-quality content and your score drops, making it harder for future emails to reach the inbox.
Email Authentication: The Foundation
Proper email authentication proves to receiving servers that you are who you claim to be. Three authentication protocols matter most in 2026.
SPF (Sender Policy Framework)
SPF lists which servers are allowed to send email on behalf of your domain. When an email arrives claiming to be from you, the receiving server checks whether it came from an approved source. Setting up SPF requires adding a TXT record to your domain’s DNS settings.
Brevo provides the exact SPF record you need. You copy it into your DNS configuration and it usually takes effect within a few hours.
DKIM (DomainKeys Identified Mail)
DKIM adds a digital signature to your emails that proves they have not been tampered with in transit. This signature gets verified against a public key published in your DNS records. Like SPF, you add a specific DKIM record that Brevo generates for you.
DMARC (Domain-based Message Authentication)
DMARC tells receiving servers what to do if an email fails SPF or DKIM checks. You can instruct them to quarantine the message, reject it entirely, or deliver it anyway but report the failure. DMARC also prevents bad actors from spoofing your domain in phishing attacks.
All three authentication methods working together dramatically improve deliverability. Gmail, Outlook, and other major providers increasingly require proper authentication before they will deliver your emails.
Building and Maintaining Sender Reputation
Your sender reputation follows your sending domain and IP address. When you first start sending emails, you have no reputation — neither good nor bad. You need to build trust gradually.
Start with a warm-up period. Do not go from zero to sending 50,000 emails overnight. Begin with smaller batches to your most engaged subscribers. Gradually increase volume over several weeks as you establish a positive sending pattern.
Consistency matters. Sporadic sending patterns raise red flags. If you normally send 1,000 emails per week and suddenly send 100,000, that looks suspicious. Maintain a relatively consistent sending schedule.
Engagement signals quality. When recipients open your emails, click links, and move messages to important folders, email providers notice. These positive signals improve your reputation. Conversely, when people mark you as spam, delete without opening, or ignore your messages consistently, your reputation suffers.
List Hygiene: Keep Your List Clean
Your subscriber list quality directly impacts deliverability. Sending to invalid addresses, spam traps, or unengaged subscribers damages your reputation.
Remove hard bounces immediately. When an email address does not exist or the domain is invalid, the message bounces. Remove these addresses from your list right away because continually sending to invalid addresses signals poor list management.
Handle soft bounces carefully. Temporary delivery failures like full inboxes or server issues cause soft bounces. After several soft bounces to the same address, remove it from your list.
Suppress unengaged subscribers. Someone who has not opened an email in six months probably never will. Create a re-engagement campaign to win them back. If they still do not respond, remove them from regular sends. Sending to people who never engage hurts your overall deliverability.
Brevo automatically handles most bounce processing, but you should periodically review your contact lists and clean out unengaged subscribers manually.
Content That Avoids Spam Filters
Certain words, phrases, and patterns trigger spam filters. While there is no definitive list of banned words, some patterns consistently cause problems.
Excessive use of spam trigger words like “FREE” in all caps, “ACT NOW,” “LIMITED TIME OFFER,” “GUARANTEED,” or “CLICK HERE” raises suspicion. One or two of these phrases in context is fine. Ten of them crammed into a subject line screams spam.
All caps text anywhere in your email looks aggressive and triggers filters. Use normal sentence case for everything including subject lines.
Too many exclamation points!!! make you look desperate!!! One exclamation point per email is plenty!!!!
Image-only emails with little or no text fail most spam filters. Email providers cannot analyze what they cannot read. Always include substantial text content alongside images.
Excessive links or links to known spam domains get flagged. Keep your link count reasonable and only link to reputable websites.
Poor HTML code structure — messy formatting, unclosed tags, inline styles — can trigger spam filters designed to catch template-based spam. Brevo’s email builder generates clean code automatically, but if you are importing custom HTML, validate it first.
Sending Practices That Matter
Send only to people who explicitly opted in. Purchased email lists are almost entirely spam traps and uninterested recipients. Using them destroys your sender reputation instantly.
Make unsubscribing easy. Every email should include a clear, one-click unsubscribe link. Making it hard to unsubscribe just means people will mark you as spam instead, which hurts you far worse.
Honor unsubscribe requests immediately. The law requires processing opt-outs within 10 days, but doing it instantly is better for your reputation. Brevo handles this automatically.
Avoid sending to role-based addresses like info@, admin@, or support@. These addresses usually do not belong to real people and often function as spam traps.
Respect sending frequency preferences. If someone asks for weekly updates, do not email them daily. Brevo lets subscribers set their own frequency preferences if you enable that feature.
Monitor Your Deliverability Metrics
Track your bounce rate — the percentage of emails that failed to deliver. A bounce rate above 2% indicates serious problems. Above 5% and email providers will start blocking you.
Watch your complaint rate — how many recipients mark you as spam. A complaint rate above 0.1% is concerning. Above 0.3% and you are risking blacklisting.
Monitor open rates as an indirect deliverability indicator. If your open rates suddenly drop, investigate whether a deliverability issue is causing your emails to land in spam folders.
Use inbox placement tests. Services like Mailreach or GlockApps let you send test emails to check which folder your messages land in across different email providers. This helps you catch deliverability problems before they affect your whole list.
Using Dedicated IP Addresses
On shared IP addresses, your reputation partially depends on other senders using the same IP. If another sender on your shared IP sends spam, everyone’s deliverability can suffer.
Dedicated IP addresses give you complete control over your sender reputation, but they require higher sending volumes to maintain properly. If you send fewer than 100,000 emails per month, stick with shared IPs. The reputation of well-managed shared IPs is usually better than what a low-volume sender can achieve on a dedicated IP.
Brevo offers dedicated IPs on Professional and Enterprise plans. The decision depends on your sending volume and how much control you need.
What to Do If Deliverability Drops
First, check your authentication records. DNS changes sometimes break SPF or DKIM records. Verify that everything is still configured correctly.
Review recent campaigns. Did you change something in your content, sending pattern, or list management that might have triggered filters?
Check blacklist status. Services like MXToolbox let you see if your sending domain or IP appears on any spam blacklists. If you are listed, follow the blacklist’s removal process.
Implement a re-engagement campaign to clean your list. Send only to engaged subscribers for a few weeks while you rebuild your reputation.
Contact Brevo support. They can often see deliverability issues on their end and provide specific guidance for your situation.
Deliverability is not a one-time setup task. It requires ongoing attention to authentication, list quality, content practices, and engagement metrics. Get these fundamentals right and your emails will consistently reach the inbox where they belong.
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