Optimizing deliverability: What needs to be done?

Even the best email campaign will not succeed if the messages fail to reach the recipients. Deliverability refers to an email's ability to be successfully delivered to the recipient's inbox.

It is not enough for an email to be technically accepted; the crucial factor is that it actually appears in the inbox rather than ending up in the spam folder or being rejected by the receiving mail server.

Deliverability is influenced by numerous technical, organizational, and content-related factors. Following best practices can significantly increase the likelihood of successful delivery.

Correctly setting up authentication methods

One of the most important prerequisites for good deliverability is the correct authentication of the sending domain.

The following methods are recommended:

• SPF (Sender Policy Framework)
• DKIM (DomainKeys Identified Mail)
• DMARC (Domain-based Message Authentication, Reporting and Conformance)
  

These standards help receiving mail servers verify the authenticity of an email. Missing or incorrect authentication can result in messages being classified as spam or rejected outright.

Using a trustworthy sending domain

The reputation of the sending domain plays a crucial role in deliverability.

A good reputation is built through responsible sending practices, such as:

• Regular communication with genuine recipients
• Low complaint rates
• Few spam reports
• Clean recipient lists
• Correct technical configuration
  

Domains with a poor reputation are scrutinized much more strictly by email providers.

Sending only to valid recipient addresses

Sending emails to outdated or invalid addresses can significantly damage your reputation. That is why recipient lists should be maintained regularly:

• Remove undeliverable addresses
• Correct typos
• Review inactive contacts
• Process unsubscribes promptly
  

An up-to-date, well-maintained recipient list improves both deliverability and campaign performance.

Use double opt-in

The double opt-in process ensures that recipients have actively signed up to receive emails.

In this process, the user confirms their subscription via a link in an email.

Benefits:

• Higher data quality
• Fewer complaints
• Fewer spam reports
• Better deliverability
• Legally compliant sign-up
  

Double opt-in is considered a proven standard for professional email communication.

Avoid spam complaints

Every spam report negatively impacts a sender's reputation.

To reduce complaints, you should:

• Send only relevant content
• Email only opted-in recipients
• Choose appropriate sending frequencies
• Use a clearly recognizable sender identity
• Meet recipient expectations
  

Recipients should always be able to understand why they are receiving a message.

Enable easy unsubscription

A visible and functional unsubscribe link is essential for any professional email.

Recipients who no longer wish to receive messages should be able to unsubscribe with just a few clicks.

A straightforward unsubscription process reduces:

• Spam complaints
• Recipient frustration
• Negative impacts on reputation
  

Ignoring or complicating unsubscribe requests significantly increases the likelihood of spam reports.

Craft content carefully

Email content also influences deliverability.

Avoid the following, for example:

• Exaggerated promotional claims
• Misleading subject lines
• Excessive use of capital letters
• An unnatural number of special characters
• Obvious spam keywords
  

Key principles include:

• Clear added value
• Understandable language
• Professional phrasing
• Content relevant to the target audience
  

Consider the text-to-image ratio

Emails consisting solely of images are often flagged by spam filters.

Recommendations include:

• Including sufficient text content
• Using images to complement the text
• Providing important information in text format as well
• Including alt text for images
  

This ensures emails remain understandable even if images fail to load.

Maintain consistent sending patterns

Email providers monitor the sending behavior of domains and mail servers. Positive indicators include:

• Consistent mailing volumes
• Predictable mailing intervals
• Steady growth
• Stable mailing activity
  

Conversely, sudden, massive mailings from domains that have seen little prior use may be flagged as suspicious.

Gradually build up new domains and servers

New sending domains and mail servers initially lack a sending history.

Therefore, it is advisable to build reputation gradually:

• Start with small mailing volumes.
• Increase mailing volume incrementally.
• Monitor recipient engagement.
• Avoid complaints and delivery failures.
  

This process is often referred to as "domain warming" or "IP warming."

Monitor delivery and error reports

Regularly checking mailing statistics helps identify issues early on.

Key metrics include:

• Delivery rate
• Open rate
• Click-through rate
• Bounce rate
• Spam complaints
• Unsubscribe rate
  

Anomalies or significant changes can indicate technical issues or problems with content.

Consider mobile optimization

Since a large proportion of emails are read on smartphones, every message should be optimized for mobile devices.

Key aspects:

• Readable font sizes
• Responsive design
• Easily accessible buttons
• Optimized images
• Short subject lines
  

A positive user experience boosts engagement and improves the sender's reputation in the long run.

Test emails before sending

Emails should be tested before launching large-scale campaigns.

It is recommended to test across:

• Outlook
• Gmail
• Apple Mail
• Mobile email apps
• Various browsers and devices
  

Testing helps identify display issues, broken links, or technical errors in good time.