Marketo Email Deliverability | How To ALWAYS Go To Inbox

Marketo Engage is a powerful marketing automation platform — but power means nothing if your emails never reach the inbox. 

The platform handles sending, tracking, and nurturing, yet deliverability depends on factors Marketo can’t control alone — your authentication setup, sender reputation, and list quality.

Average inbox placement across email providers is 83.1%. That means roughly 17% of marketing emails fail to reach their intended destination — landing in spam, promotions tabs, or vanishing entirely. 

For Marketo users sending hundreds of thousands of emails monthly, that failure rate translates to significant lost revenue.

To ensure your Marketo emails reach the inbox, you have to focus on:

• Sender reputation, that’s your domain, and IP trust score
• Email warmup to build a reputation for the new sending infrastructure
• List hygiene, including bounce management and engagement filtering
• Authentication protocols like SPF, DKIM, and DMARC configuration
• Monitoring and tracking metrics that signal problems early

In this article, we’ll dive deeper into each area and show you how to improve your Marketo email deliverability: 

Why do Marketo emails land in spam?

Emails land in spam when ISPs detect signals that indicate unwanted or suspicious messages. 

Marketo provides the infrastructure, but your configuration and sending practices determine whether Gmail, Outlook, and Yahoo trust your emails enough to deliver them.

The most common culprits fall into three categories (and often, problems compound — one issue triggers another, creating a downward spiral).

Authentication gaps

Missing or misconfigured authentication tells receiving servers they can’t verify your identity. Without SPF and DKIM, your emails look suspicious — anyone could be spoofing your domain. Google and Yahoo now require authentication for bulk senders — emails without it are automatically filtered or rejected.

Marketo handles some authentication automatically, but you’re responsible for DNS records. A common mistake: setting up SPF/DKIM for your primary domain but forgetting subdomains, or failing to implement DMARC entirely.

Reputation damage

Domain reputation and IP reputation accumulate over time based on recipient behavior. High complaint rates, low engagement, and spam trap hits tank your reputation — and recovery takes weeks or months.

Marketo’s shared IP pools present additional risk. If other senders on your shared IP behave badly, their reputation damage affects your deliverability. This is why high-volume senders often upgrade to dedicated IPs (though dedicated IPs require sufficient volume to maintain).

List quality

Purchased lists, outdated contacts, and inactive subscribers result in bounces, complaints, and spam-trap hits. ISPs interpret these signals as evidence that you’re sending unwanted email — regardless of how valuable your content actually is.

A bounce rate above 2-3% signals list problems. Spam complaint rates above 0.1% (Google’s threshold) trigger filtering. Both metrics require active management within Marketo.

How do you set up authentication in Marketo?

Authentication proves you’re authorized to send from your domain. Proper setup is non-negotiable — it’s the baseline requirement before any other deliverability optimization matters.

SPF and DKIM

Marketo provides SPF and DKIM configuration in Admin > Email > SPF/DKIM. The platform generates the DNS records; you add them to your domain’s DNS.

Protocol	What it does	Marketo location
SPF	Authorizes Marketo’s servers to send for your domain	Admin > Email > SPF/DKIM
DKIM	Cryptographically signs emails to prove authenticity	Admin > Email > SPF/DKIM

After adding DNS records, verification typically takes 24-48 hours. Check status in Marketo’s admin panel — green checkmarks indicate successful setup.

Critical detail: verify all sending domains. If you send from marketing@company.com and newsletter@brand.company.com, both domains need authentication. Missing one creates a gap that hurts deliverability for everything.

DMARC

DMARC coordinates SPF and DKIM, telling receiving servers what to do when authentication fails. Marketo doesn’t manage DMARC directly — you configure it in your DNS.

Start with a monitoring policy (p=none) to collect data without affecting delivery. After analyzing reports (typically 2-4 weeks), move toward enforcement (p=quarantine, then p=reject). For detailed guidance, see our DMARC setup guide.

How do you monitor sender reputation?

Reputation problems often develop silently — you won’t notice until delivery rates drop significantly. Proactive monitoring catches issues early, when they’re easier to fix.

Google Postmaster

Google Postmaster Tools provides Gmail-specific reputation data. After verifying your domain, you’ll see:

• IP reputation (same scale)
• Authentication success rates
• Domain reputation (High/Medium/Low/Bad)
• Spam rate (percentage of emails marked as spam)

A sudden shift from “High” to “Medium” reputation warrants immediate investigation. Check recent campaigns for unusual bounce rates, complaints, or content changes that might have triggered filtering.

Microsoft SNDS

Microsoft SNDS (Smart Network Data Services) offers similar visibility for Outlook. 

The interface is less intuitive than Google’s, but the data is equally valuable for enterprise senders with significant Outlook audiences.

SNDS requires dedicated IP addresses — shared IP users can’t access individual reputation data (another reason high-volume senders consider dedicated IPs).

Marketo reports

Within Marketo, the Email Performance Report reveals engagement patterns that affect reputation:

Metric	Healthy target	Warning sign
Delivered	98-99%	Below 95%
Opened	>20%	Below 15%
Click-to-open	>15%	Below 10%
Unsubscribed	<0.2%	Above 0.5%

Create a report for all emails sent in the past 90 days. Look for outliers — campaigns with significantly worse metrics than your average indicate specific problems worth investigating.

Enable bot activity filtering (Admin > Email > Bot Activity) to remove automated clicks from your data. Without filtering, bot activity inflates metrics and obscures real engagement patterns.

How do you manage bounces and list hygiene?

Bounces signal list quality problems. Hard bounces (permanent failures) indicate invalid addresses. Soft bounces (temporary failures) become concerning when they repeat — suggesting the recipient’s server consistently rejects your emails.

Bounce programs

Marketo’s deliverability management requires smart campaigns that identify and suppress problematic addresses. The standard approach:

Campaign	Trigger	Action
Hard bounce handler	Email bounced (hard)	Marketing suspended = true
Soft bounce handler	Email soft bounced 3x in 60 days + not delivered 3x in 60 days	Marketing suspended = true
Invalid email handler	Email invalid = true	Exclude from sends

The soft bounce logic is important — a single soft bounce might be temporary, but three failures without successful delivery indicate a persistent problem. Continuing to send damages your reputation without reaching anyone.

Engagement filtering

Low engagement hurts reputation even when emails are technically delivered. ISPs watch whether recipients open, click, and reply — or ignore and delete.

Create a “Marketable Emails” smart list excluding invalid addresses, hard-bounced contacts, unsubscribed contacts, and anyone with no engagement in 6+ months. 

Sending only to engaged contacts improves metrics, which in turn improves reputation, which in turn improves deliverability — a positive compound effect.

For deeper list management strategies, see our email list hygiene guide.

Should you use a dedicated IP in Marketo?

Dedicated IPs isolate your reputation from other senders. Marketo offers dedicated IPs as an add-on (available in the Advanced edition), but they’re not universally beneficial.

Factor	Shared IP	Dedicated IP
Cost	Included	Additional fee
Reputation control	Shared with others	Fully yours
Volume requirement	None	100K+ monthly recommended
Warmup needed	No	Yes (critical)
Best for	Lower volume, consistent sending	High volume, variable patterns

Dedicated IPs make sense when:

• You send 100,000+ emails monthly
• Shared IP reputation issues have affected you
• You need reputation isolation for compliance reasons
• Your sending patterns vary significantly (promotional spikes)

The critical caveat is that new dedicated IPs start with a reputation of 0. Sending high volume immediately triggers spam filtering. Proper warmup is mandatory — gradually increasing volume over 2-4 weeks while building positive engagement signals.

What about email warmup for Marketo?

New sending domains, new IPs, and reputation recovery all require warmup — gradually building the trust that ISPs use to determine inbox placement. Marketo doesn’t include built-in warmup functionality; you’re responsible for managing the process.

Warmup fundamentals for Marketo users:

1. Start with 10-20 emails daily to highly engaged contacts
2. Increase volume by 15-20% every few days
3. Monitor bounce rates and complaints closely
4. Pause and investigate if metrics spike negatively
5. Expect 2-4 weeks before reaching full volume

The challenge is that generic warmup emails look artificial to ISPs. They recognize patterns that don’t match real business communication — and flag them accordingly.

Email warmup works better when it mimics your actual campaigns

EmailWarmup.com’s personalized warmup analyzes your sending patterns and replicates them naturally, building a reputation that transfers to your real campaigns. 

For Marketo users launching new sending infrastructure or recovering from reputation damage, personalized warmup can achieve inbox rates of up to 98%.

Before launching any Marketo campaign, run a free email deliverability test across 50+ providers. You’ll see exactly where emails land — inbox, spam, or promotions — before your actual subscribers become test subjects.

If you’re struggling with persistent Marketo deliverability issues, EmailWarmup.com offers free deliverability consultations with human specialists (available 24/7) who can audit your setup and recommend specific fixes.

Frequently asked questions

Here are some commonly asked questions about Marketo email deliverability: