Fixing email deliverability and spam issues

Q: Domain reputation issues

Poor domain reputation. Sending to purchased lists or invalid addresses, or spam-like behavior, can harm your domain's reputation. This may lead to blocklisting or spam filtering, which affects the deliverability of even regular one-to-one emails. Recipient behavior. If recipients often mark your messages as spam, delete them without reading, or unsubscribe at unusually high rates, mailbox providers take it as a sign that your emails are unwanted. This can hurt both your domain and IP reputation, and reduce your overall email deliverability.

Q: DNS configuration issues

SPF (Sender Policy Framework). SPF records declare which mail servers are authorized to send email for your domain. Misconfigured or overly complex SPF records can cause delivery failures or spam filtering. DNS lookup limit. SPF records are limited to 10 DNS lookups. Going over this limit makes SPF validation fail. Opensense offers an SPF flattening solution that reduces DNS lookups and keeps your SPF record compliant with the RFC standard. For details, contact your dedicated Opensense account manager. DKIM and DMARC. A DKIM (DomainKeys Identified Mail) or DMARC (Domain-based Message Authentication, Reporting, and Conformance) failure can flag emails as possibly spoofed or unauthenticated.

Q: Content and formatting triggers

High image-to-text ratio. Emails with more images than text are common spam indicators. Keep at least 60% text and no more than 40% images. Around 70% text to 30% images is ideal for deliverability. Problematic hyperlinks. Broken, suspicious, or non-secure (non-HTTPS) links raise red flags for spam filters, especially links on unrelated domains or link shorteners (for example, Bitly or TinyURL). HTML structure. Overuse of tables, excessive whitespace, malformed HTML, or large signature blocks can trigger spam filters. External media. Static images or banners hosted on unverified domains can hurt sender reputation.

Overview

If your team’s emails are going to recipients’ spam or junk folders, or not being delivered at all, while you use Opensense email signatures or banner campaigns, it helps to understand the technical and content factors that influence email deliverability.

Opensense and deliverability

Opensense is committed to deliverability and security. All signature images and banner assets are white-labeled to your organization’s domain, for brand consistency and domain alignment. We test rigorously, and follow email authentication standards.

Opensense supports over 500 SMB and enterprise clients, including Fortune 500 companies and multinational organizations. Deliverability is our top priority, and you can be confident that your signatures and banners are deployed securely and professionally.

Even so, email deliverability also depends on factors outside Opensense’s infrastructure. These are the most common reasons emails are marked as spam.

Why emails end up in spam

Domain reputation issues

Poor domain reputation. Sending to purchased lists or invalid addresses, or spam-like behavior, can harm your domain's reputation. This may lead to blocklisting or spam filtering, which affects the deliverability of even regular one-to-one emails.
Recipient behavior. If recipients often mark your messages as spam, delete them without reading, or unsubscribe at unusually high rates, mailbox providers take it as a sign that your emails are unwanted. This can hurt both your domain and IP reputation, and reduce your overall email deliverability.

DNS configuration issues

SPF (Sender Policy Framework). SPF records declare which mail servers are authorized to send email for your domain. Misconfigured or overly complex SPF records can cause delivery failures or spam filtering.
DNS lookup limit. SPF records are limited to 10 DNS lookups. Going over this limit makes SPF validation fail. Opensense offers an SPF flattening solution that reduces DNS lookups and keeps your SPF record compliant with the RFC standard. For details, contact your dedicated Opensense account manager.
DKIM and DMARC. A DKIM (DomainKeys Identified Mail) or DMARC (Domain-based Message Authentication, Reporting, and Conformance) failure can flag emails as possibly spoofed or unauthenticated.

Content and formatting triggers

High image-to-text ratio. Emails with more images than text are common spam indicators. Keep at least 60% text and no more than 40% images. Around 70% text to 30% images is ideal for deliverability.
Problematic hyperlinks. Broken, suspicious, or non-secure (non-HTTPS) links raise red flags for spam filters, especially links on unrelated domains or link shorteners (for example, Bitly or TinyURL).
HTML structure. Overuse of tables, excessive whitespace, malformed HTML, or large signature blocks can trigger spam filters.
External media. Static images or banners hosted on unverified domains can hurt sender reputation.

Blocklisting and DNS issues

Your domain or IP may be on public DNS blocklists because of past email activity. To help resolve deliverability issues, have your IT team check:

Domain blocklisting. Whether your domain or IP is on common DNS-based blocklists (for example, Spamhaus, Barracuda, or SORBS).
DNS configuration errors. That records like A, MX, and PTR are configured properly and resolve correctly.
Mail server responsiveness. That your mail server reliably accepts connections, and isn't timing out or rejecting traffic.
SPF, DKIM, and DMARC records. That these authentication protocols are set up correctly and aligned, to protect your domain from spoofing.

Improving deliverability

Work through these best practices with your IT team.

Review email headers

Ask your IT team to inspect the headers of messages that were marked as spam. These headers can help show why an email failed authentication or deliverability checks:

Authentication-Results
Received-SPF
DKIM-Signature
ARC-Authentication-Results

Make sure that:

All links begin with https://.
They include www. where applicable.
They don’t use link shorteners, like Bitly or TinyURL.
Assets are hosted on your domain, or your white-labeled subdomain.

Missing www. or unsecured links can increase your spam score.

Authenticate your email domain

Check that your domain has these configured properly:

SPF: Authorizes which servers can send email for you.
DKIM: Adds a digital signature to verify that the email is authentic.
DMARC: Says how to handle emails that fail SPF or DKIM checks.

See Required DNS settings for Opensense and Verifying your Opensense DNS records.

Monitor your sending practices

Keep email lists clean, and remove invalid addresses regularly.
Avoid sudden spikes in email volume.
Make sure that recipients have opted in to your communications.
Make it easy for recipients to unsubscribe.

When to contact Opensense

If you’ve checked everything above, and still have deliverability issues, contact help@opensense.com right away, with example email headers or timestamps. We’ll investigate, and resolve any issues within our control or infrastructure.