Anyone who does email marketing has likely encountered this situation: you spend most of the day writing a promotional email, with beautiful layout, excellent copywriting, and great discounts, and then send it out to everyone, eagerly waiting for the data—only to find that the open rate is less than 1%.
It's not that your email was poorly written, nor that the customer wasn't interested in your product. The real reason is that your email never even appeared in the customer's inbox ; it lay quietly in the spam folder, or was even blocked by the mail server, never even making it to the spam folder.
The key factor behind this is called sender reputation .
What exactly is the credibility of email sending?
You can think of email reputation as a "credit score." Just like banks give you a credit score based on your repayment history, email service providers like Gmail, Outlook, and Yahoo also score each sender.
This score determines how your sent emails will be processed:
- High score → Directly sent to inbox
- Average score → Go to the "Promotion" or "Sale" tab
- Low score → Go to the trash can
- Extremely low score → directly rejected by the server, emails disappear without a trace.
The problem is that you can't see the specific numerical value of this score, and the email service provider won't tell you it proactively. You can only infer your creditworthiness through indirect indicators such as delivery rate and open rate.
How is the credit score calculated?
Different email service providers use different algorithms, but their core considerations are basically the same. Let's discuss them one by one.
bounce rate
This is the most directly impactful metric. If you send 1000 emails and 80 are bounced back, that's an 8% bounce rate. The industry-recognized safe line is below 2% ; anything above 5% will generally attract attention.
What does a high bounce rate indicate? It indicates that your email list is of poor quality—it contains a large number of non-existent addresses, deactivated email addresses, and misspelled addresses. Your email service provider will assume you are either sending spam or simply don't care who the recipients are.
This is the easiest problem to solve, and also the one that many people tend to overlook. Before sending, run an email verification tool like AcctCheck through the list to remove invalid addresses, and the bounce rate will immediately decrease.
Complaint rate
When a recipient clicks the "Report Spam" button, that counts as one complaint. The safety threshold for the complaint rate is very low— 0.1% , meaning that for every 1,000 emails sent, there can only be a maximum of one complaint.
Many people think, "I'm not sending a scam email, who would report me?" The reality is, when users are too lazy to find the unsubscribe link, clicking the report button is much easier than finding the unsubscribe button. Therefore, your unsubscribe link must be obvious and easy to find; don't hide it at the very bottom of the email in small gray font (size 6).
Another common scenario is that a user did subscribe to your emails two years ago and has long forgotten about it. Suddenly receiving a promotional email from you, their first reaction is, "Who is this? I didn't subscribe to this!"—and then they report it. Therefore, it's best to send a confirmation email to users you haven't contacted in a long time before resending.
Interaction rate
Email service providers monitor the interaction between recipients and your emails: whether they opened them, clicked links, replied, or added you to their contacts.
If most people don't open your emails, and the few who do open them don't click on them, your email service provider will consider your emails worthless. Over time, even if the addresses are valid and no one complains, your emails will slowly end up in the spam folder.
Conversely, if the recipient frequently opens your emails, clicks on links within them, and occasionally replies to you, then you have a very good reputation with that recipient, and subsequent emails will almost certainly reach their inbox.
Sending volume and frequency
A sudden surge in email volume is a strong negative sign. Sending 200 emails a day when you normally do, and then suddenly sending 20,000—this is highly consistent with the behavior patterns of spammers in the eyes of email service providers.
Similarly, the frequency of sending emails is also important. Sending three emails to the same group of users every day versus sending one email per week will have drastically different results. The former is more likely to lead to a surge in complaints and unsubscribes.
Infrastructure configuration
This is somewhat technical, but not complicated. It mainly involves three things:
- SPF — Tells the receiving mail server "which IPs are authorized to send emails on behalf of my domain".
- DKIM — Add a digital signature to your emails to prove that the content has not been tampered with.
- DMARC — Defines how the receiving server should handle SPF or DKIM authentication failures.
If these three elements aren't matched correctly, it's like sending a letter without a signature, without a stamp, and even the sender's address on the envelope is handwritten. Why should the recipient believe that the letter was sent by you?
The good news is that these three configurations only need to be done once. The bad news is that many people have no idea they need to do this.
Two types of reputation: IP reputation and domain reputation
The credibility of a message actually has two layers, which many people confuse.
IP reputation is tied to the IP address of the server sending the emails. If you're using a third-party platform like Mailchimp or SendGrid, multiple clients may share the same IPs. This means that other people's sending activities will also affect you. If a provider sharing your IP is sending spam in bulk, you'll also be affected. This is why it's recommended to apply for a dedicated IP once you've reached a certain sending volume.
Domain reputation is tied to your sending domain, such as @yourcompany.com . This reputation follows the domain and cannot be taken away by changing your IP address. In recent years, email service providers have increasingly emphasized domain reputation, especially Gmail, where domain reputation now carries more weight than IP reputation.
Therefore, even if you change the sending platform or the IP address, if the domain has a poor reputation, the emails will still end up in the spam folder.
How can I tell if I have good or bad credit?
Although you can't see the specific score, there are a few free tools that can help you get a general idea of the situation:
- Google Postmaster Tools — If you have a large number of Gmail users in your recipients, this tool can tell you key metrics such as domain reputation, IP reputation, complaint rate, and verification status, and it's completely free. Everyone doing email marketing is highly recommended to register for one.
- Microsoft SNDS — a similar tool targeting Outlook/Hotmail users.
- MXToolbox — Check if your IP address and domain name are on various blacklists.
Additionally, pay attention to your own sending data. If the delivery rate of your recent mass emails has been consistently declining, and the open rate has inexplicably decreased, it's very likely that there's a problem with your credibility.
Its reputation is already terrible, is there any hope for it?
There is hope, but it requires patience. There are no shortcuts to restoring reputation; the basic logic is to gradually pull your score back through consistent positive messaging behavior.
Step 1: Suspend large-scale transmission
Stop sending mass emails using the existing list. Every additional batch of problematic emails will further damage your credibility.
Step 2: Thoroughly clean up the email list
Go through the entire list using an email verification tool:
- Invalid address → Delete all
- One-time email address → Delete all
- Character emails (info@, admin@) → Group or delete separately
- Emails that haven't been opened in more than 6 months → Move to the "Inactive" group
After cleaning, only active users who have recently interacted with the system will be retained.
Step 3: Preheat in small amounts
Start with 20-50 emails per day, sending only to the most active users—those who frequently open your emails and click on links. These are the people most likely to interact with you, helping you rebuild positive interaction data.
Gradually increase the daily sending volume over 2-4 weeks. During this period, closely monitor bounce rate and complaint rate to ensure they remain within safe limits.
Step 4: Check and repair technical configuration
Take this opportunity to check SPF, DKIM, and DMARC. If they weren't configured before, configure them now. If they were configured but have errors, correct them.
Step 5: Continuous monitoring
Reputation restoration is not a one-time event. It requires consistent weekly checks of Google Postmaster Tools data, regular cleanup of the posting list, and maintaining a stable posting frequency. This is a long-term commitment.
Prevention is much easier than repair.
Having discussed so many repair methods, the truly smart approach is to avoid ruining your reputation in the first place. Here are a few key habits to summarize:
- Verify email addresses before sending – Verify each new batch of addresses before sending; this step can directly reduce the bounce rate to below 1%. AcctCheck supports batch verification; simply upload the list to run it.
- With Double Opt-in , after the user enters their email address, a confirmation email is sent first, and the subscription is officially completed only after the user clicks the confirmation link. It's a bit more troublesome, but the list quality is much higher.
- Placing the unsubscribe link in a prominent position —making it easy for people who don't want to receive emails to unsubscribe—is a million times better than making them click a report button.
- Control the sending frequency —don't send too frequently. One to two emails per week is reasonable for most industries.
- Clean up your list regularly —at least once a quarter. A larger list isn't necessarily better; activity level is key.
- New domains/IPs need to be warmed up beforehand —don't send out tens of thousands of emails on the first day of registering a new domain; you must start with a small amount and gradually increase.
In conclusion
The effectiveness of email marketing hinges on the fundamental factor of sender credibility. Unlike the email subject and body, which are readily apparent, it determines whether your email ever gets a chance to be seen. No matter how well-written the subject line is, if your credibility is lacking, customers won't even get a glimpse of it.
Fortunately, reputation management isn't complicated; it boils down to three things: keeping your email list clean, ensuring proper technical verification, and maintaining consistent sending habits . If you do these three things well, your emails will reliably appear in your customers' inboxes.