The Concept of Micro-Deliverability in Email Marketing [2022]

Micro-Deliverability is a relatively new concept in the email marketing domain. It involves drilling down into deliverability by domains, or ISPs or SMTP Relay servers and then segmenting the email list or campaigns based on the results to get best deliverability and performance for the marketing campaigns.

The best SMTP relay service providers have the overall deliverability rates of above 96%, but these deliverability rates keep on fluctuating based on ISPs as well as time. By carefully tracking these fluctuations of deliverability trends based on ISPs and time, one can route their emails for different segments using SMTP delivery servers that deliver the best performance for that particular segment.

Thus, using more than one email delivery system (Hybrid System) can significantly enhance your email marketing performance.


By redundancy, we mean, having more SMTP relay servers ready for use than you actually use. This redundancy can be a great asset to have at the worst of times. When there is a temporary outage or significant drop in deliverability for a specific SMTP relay server (for a particular segment), redundancy gives you the flexibility to immediately switch the relay server for that segment without impacting performance and deliverability.

Email Filtering by ISPs and Deliverability Issues

Email filters are a fact of life, especially for an email marketer. They are a necessary evil to filter out spam. But sometimes, legitimate email messages are mistakenly filtered as spam or sent into junk box. This is the collateral damage of email filters. The sender’s reputation causes many deliverability issues, but some issues are related to the SMTP relay service providers too.

Why Email Filters are required in the First Place?

According to Symantec, nearly 70% of all email sent is spam.

These include phishing messages, malware, emails coming from spammers who leverage this channel for nefarious purposes. If no filter existed, all these emails would be delivered to the inbox. For every useful email, there will be two spam emails. This would make the whole email channel useless. Email spams are the reason the ISPs filter emails.

Causes of Email Deliverability Issues

There are multiple reasons why a legitimate email ends up in a spam folder rather than the inbox. Some of these are related to the sender’s reputation while others are related to the email service provider the sender is using.

Still Not a User of EasySendy Pro for Hybrid Email Campaigns?

[bctt tweet=”Authentication, Bounce & Complaint Management, IP Reputation are the major cause of Email Deliverability Issues.” username=”easysendy”]

Sender Issues

Sender’s reputation is considered in deciding whether an email will reach an inbox or the spam folder. Multiple factors determine the sender’s reputation. These factors are as mentioned below:


ISPs rely heavily on authentication to make sure that the stated sender is the actual sender of the email. Three different authentication methods are used by the ISPs to do the authentication:

  • Sender Policy Framework (SPF)
  • Sender ID
  • Domain Keys Identified Mail (DKIM)
  • Domain Message Authentication Reporting & Conformance (DMARC)

These authentication methods allow the ISPs to compare email information with the DNS records about the email sender. If the email information does not match the DNS information, there are more chances of the email landing in the recipient’s spam box rather than the inbox. If the sender’s authentication is not in place, the sender’s reputation will deteriorate.

2. Spam Complaints

If the recipients are reporting sender’s emails as spam, the sender’s reputation will deteriorate. Spam complaints should be less than 0.1% of the total sent volume for every email. If this rate is more than the 0.1% on a consistent basis, the sender’s reputation is bound to deteriorate.

3. Bounce Management

Repeatedly getting their emails bounced will reduce the sender’s reputation. It shows the ISPs that the sender’s email list is not clean. The industry standard is to remove hard bounces after one occurrence and soft bounces after three consecutive sends.

4. Recipient Engagement

A sender’s reputation gets damaged when the recipients to whom the sender is sending emails aren’t opening those emails. In other words, the clicking/ opening rates are low. This detail shows that the recipients to whom the sender is sending emails are not interested enough in those emails.

SMTP Relay Issues

There are SMTP relay issues due to which the email deliverability might get hampered. The most common problem is related to shared IP addresses. Although the ISPs are moving towards domain-specific filtering, most ISPs still filter at an IP address level. This means that if an IP address is sending emails which are perceived to be spam, all emails from that IP address will be blocked regardless of the domain it is sent from. Even from a dedicated IP address, which is used by a single entity, one can experience SMTP relay side deliverability issues.

Hindrances to achieve Optimized Micro-Deliverability

1. Scarcity of Micro-Deliverability Data

SMTP relays publish their overall deliverability rates on a monthly or a quarterly basis. They do not have resources to post them more frequently. Even in these publications, the deliverability rates are overall rates, not by Domains/ISPs. These overall rates cannot be used for Micro-Deliverability optimization purposes.

2. Lack of Time

Even if the data would have been available for Micro-Deliverability Optimization purposes, the time taken to arrange that data and then use it for email segmentation purpose is unfeasible for the email marketers to carry them practically out.

3. Single ESP or SMTP Model

Most organizations tend to have a single ESP or SMTP model. This is because learning and using multiple ESP or SMTP relay interfaces, sending emails from multiple SMTP interfaces and aggregating the performance data from each one of them is time-consuming and unfeasible, to say the least.

About EasySendy PRO

EasySendy Pro is an email marketing platform for the digital marketing team. It integrates with multiple SMTP relay service providers and enables delivery of email campaigns to a list of opt-in emails. You can split test email deliveries across the relay servers and check reports, track email clicks, opens of each email campaign. It also has smart autoresponder and email list segmentation.

To support Micro-Deliverability in Emails; currently, EasySendy Pro allows integration with SMTP relay gateways like Amazon SES, Mandrill, SendGrid, Sparkpost, Leadersend, Dyn, Elasticemail, MailGun, SendinBlue, MailJet, TipiMail, and MailerQ. If you are sending an email to a list of above 25,000 email subscribers, then, Micro-deliverability of the email through multiple SMTP gateways provide better email open rate.

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