Sender reputation

Advertising email campaigns earned a negative reputation almost from their inception (with the first advertisements appearing in the 1990s) due to spam.

The primary themes of spam emails during that time included advertising low-quality products, invitations to participate in fraudulent schemes, and messages containing viruses. Gradually, the number of such emails decreased with the help of laws protecting internet users' rights.

Averse to email advertising, users struggled to distinguish between spam and legitimate advertising from regular senders, leading to a decrease in trust in all electronic mail over time.

Consequently, users often marked emails as spam without scrutinizing their content, a behavior observed by mail services. These services remembered your "reputation" among customers.

However, mail services not only consider user reactions to mailings but also analyze the content of emails, the type of distribution, and search for spam words.

Therefore, to ensure the success of an email campaign, it is essential to first establish your reputation on the server where you plan to send the emails.

What is sender reputation

Sender reputation is a rating or evaluation assigned by mail providers to email senders based on various factors. When a request for email delivery is received, servers analyze the sender's reputation. Based on this analysis, they decide whether to route the email to the spam folder or the inbox. Sender reputation consists of both IP and domain reputation and is calculated by mail servers using algorithms.

A good sender reputation allows for:

  • Increased email deliverability.

  • Building trust in the company through quality mailings.

  • Protecting users from fraudsters. A brand with a good reputation is more challenging for spammers to impersonate.

Factors influencing sender reputation

Factors influencing sender reputation vary and are interconnected. They include:

1) Hard bounce and soft bounce

Bounce refers to the situation when an email fails to reach the recipient's mailbox for various reasons.

This parameter directly impacts reputation. Mail servers recognize undelivered emails, interpreting them as spam protection.

Hard bounces, occurring due to incorrect email addresses, inactive accounts, or spam traps, raise the most suspicion.

Altcraft Platform automatically adds addresses to a global stop list after a hard bounce, preventing further email delivery.

Soft bounces, caused by server errors or heavy emails, have a lesser impact on reputation. They occur when emails fail to reach due to server errors or excessively large messages.

2) Sender history

It includes the number of emails you've sent in the past, frequency of sending, and email content. Sending a large volume of emails in a day is considered suspicious. Also crucial is the nature of the emails sent to recipients: whether they are spam or resemble it.

3) Customer engagement

High engagement entails a significant percentage of email opens and clicks. Replies and forwards also enhance reputation. However, if users consistently ignore your emails, it lowers your rating. The worst scenario for an advertising campaign is email deletion and spam complaints.

4) Spam complaints

An essential metric that rapidly degrades sender reputation. If users frequently report your emails as spam, email servers may conclude that you are sending content to users who haven't consented to it. It could be perceived as distributing viral or illegal content.

In Altcraft Platform, the subscription status of a profile that reports spam changes to "Complainer."

Spam complaint

Campaigns do not send messages to profiles with such status. If the complaint rate in an account exceeds 0.07% within one hour, users will receive a notification via email. This helps promptly address a hazardous situation. The complaint rate is the ratio of the number of complaints to the number of delivered emails.

5) Falling into spam traps

Spam traps are fake email addresses or servers created to track spam. They belong to individuals who no longer use email or are entirely synthetic addresses. They are often publicly available within email address lists for sale. When spam is sent to such addresses, the sender's reputation instantly decreases.

To avoid falling into spam traps, it's essential to "cleanse" the email address database. A "clean" database of active clients prevents reputation deterioration (and increases engagement chances).

6) Presence of IP address or domain in blacklists

If an IP address or domain is listed in public blacklists (not a private list owned by one user), emails may be blocked by most email addresses at once.

Notification of being blacklisted typically arrives via email or server response. This can happen due to inactive client addresses, turning their accounts into spam traps. Sending emails to such addresses may lead verification systems to consider you a spammer.

Mail servers may remove a company from a blacklist if it was listed accidentally once. However, repeated listings may result in no removal from the blacklist.

7) Unsubscriptions

Mass unsubscribes (not only from inactive clients but also from long-standing subscribers) indicate that the email campaign is irritating users. If you notice increased unsubscribing, check the quality of your emails and the presence of spam-like content.

Mail servers monitor user reactions. Unsubscriptions draw their attention and decrease the sender's reputation.

8) Email authentication

Configuring authentication informs mail servers that your domain is reliable and emails come from a verified source, not spammers.

This also protects against domain theft and email forgery. If mail servers detect spam sent from your name, they may decrease your reputation or blacklist your domain.

How to check your reputation

Using reputation checking services allows you to monitor changes and user reactions to content. If you notice that some emails are being forwarded by clients while others are flagged as spam, consider adjusting your campaign strategy.

1. Mail-Tester

Send your email to a random address provided on the page to analyze for spam.

Check domain reputation with Mail-Tester

The spam analysis is done within seconds. Three free checks are available without authentication, and registered users get 20 checks.

Mail-Tester results

2. SenderScore

This service checks the reputation of the sending domain and SSL certificate. Data are based on the average value over 30 days and display the rating of your IP address.

Check domain reputation with Sender Store

3. BarracudaCentral

The service has its own Barracuda reputation system—a database of domains and IP addresses checked in real-time. To evaluate, enter the IP address into the database, then check it on the main page.

Check domain reputation with Barracuda

Improving sender reputation

You can improve your reputation in several ways. Here are the main ones:

Method 1: check the address list.

Exclude all invalid email addresses: addresses with errors, spam traps, unused addresses, addresses that do not open or complain about emails.

To check addresses, use one of these servers:

Keep active ones: those belonging to real users, potential customers (people who have confirmed their desire to receive the newsletter), and people who open emails.

Here’s the example of how to do this using the platform:

How to check the address list

Hint: Two-step subscription will help you with this. It's called "Double Opt-In," where the user not only provided their email address but also clicked on a special link and confirmed their consent to receive information from the sender. You can read more about this in our article.

Method 2: work on the content

Quality content affects engagement. If your email has already been delivered and the server hasn't flagged your domain as malicious, it's important to attract and retain the customer's attention.

If your emails are useful, noticeable (not due to all caps and "yellow" advertising headlines), and allow users the right to receive the newsletter or not, then the reputation will increase.

In addition to the basic rules of absence of viruses inside the email, sales of low-quality or illegal goods and services, there are other requirements for high-quality mailing. For example, writing "live" subject lines and pre-headers or avoiding stamps and "spam" words in the body of the email.

Method 3: warm up your IP address

A newly acquired IP is "cold." You can make it "warm" by gradually increasing the number of sent emails and the frequency of sending. This should be done slowly, otherwise services may consider the mailing as spam. It is also necessary to follow the rules mentioned above.

Method 4 — work with postmasters

The postmaster is a service for tracking the statistics of mailings within a specific mail provider. It has access to more information than regular mailing services, as it analyzes subscriber actions more deeply on one provider.

Google Postmaster:

Yahoo Postmaster:

Outlook Postmaster:

Mail Postmaster:

For example, here's what Google Postmaster looks like.

Google Postmaster

To check the mailing in this postmaster, you need to:

  • specify the domain from which the mailing is conducted;

  • confirm ownership of the domain.

After that, you will have access to check emails, view the reputation of the IP address and domain, as well as other tools for campaign analysis.

Method 5: set up FBL (Feedback Loop) reports

FBL reports are also configured with a specific email provider. With such reports, you can receive real-time information on whether users have marked emails as spam.

For example, setting up FBL in is done through

The following parameters are mainly analyzed:

  • number of sent emails

  • complaints

  • average complaint rate, from which reputation is derived

  • deleted emails

  • successfully delivered emails


Thus, sender reputation is a rating or evaluation assigned by email providers to email senders based on various factors. These factors either enhance or diminish the reputation. A good reputation increases the effectiveness of email campaigns and builds trust among users. Conversely, a poor reputation leads to decreased trust and may result in domain blocking and email sending restrictions.

Improving reputation is also a complex process. Attention must be paid to multiple factors simultaneously, as errors can lead to blacklisting with no way out.

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