How do MX records impact email bounces and sender reputation?
Matthew Whittaker
Co-founder & CTO, Suped
Published 12 Jul 2025
Updated 17 Aug 2025
8 min read
When delving into the intricacies of email deliverability, it's easy to overlook foundational elements like MX records. Many assume that as long as emails are being sent, the underlying DNS setup is working perfectly. However, misconfigurations in these crucial records can have a ripple effect, leading to increased bounce rates and a damaged sender reputation.
Email bounces are more than just failed deliveries; they are signals that internet service providers (ISPs) use to gauge the health of your sending practices. A consistently high bounce rate can severely impact how mailbox providers view your domain, often leading to your messages being flagged as spam or blocked entirely. Understanding how MX records play into this can be a game-changer for your email program.
In this article, I'll explain the specific ways MX records influence your email bounces and ultimately, your sender reputation. We’ll explore their function, common issues, and how proper configuration is essential for maintaining a healthy and effective email sending infrastructure.
Understanding MX records
MX records, or Mail Exchange records, are a type of DNS record that specifies mail servers responsible for accepting email messages on behalf of a domain name and where to route those emails. Think of them as the postal service's directory, telling other mail servers exactly where to send mail for your domain. Without them, other servers wouldn't know where to deliver incoming emails.
Each MX record includes a preference number, also known as priority. A lower preference number indicates a higher priority. When multiple MX records exist, mail servers attempt delivery to the server with the lowest preference number first. If that fails, they move to the next highest priority server. This setup provides redundancy and ensures email delivery even if one server is temporarily unavailable.
While MX records primarily govern incoming mail, their proper setup is critical for your sending infrastructure too. When you send an email, the recipient's mail server performs various checks, and a valid MX record for your sending domain (or its bounce subdomain) is often part of this validation process. It signals that your domain is legitimate and capable of receiving mail, which is a fundamental trust factor.
Example MX RecordsDNS
yourdomain.com. IN MX 10 mail.yourdomain.com.
bounce.yourdomain.com. IN MX 5 feedback.your-esp.com.
The indirect impact on email bounces
MX records don't directly cause a hard bounce (permanent failure) or soft bounce (temporary failure) themselves. These typically occur when mail servers attempt to deliver an email and encounter an issue, such as a non-existent recipient or a full mailbox. The direct interaction between the sending and receiving mail servers usually handles these bounces within the SMTP dialog. However, MX records become critical when bounce notifications (also known as Non-Delivery Reports or NDRs) need to be sent back to the original sender.
When a recipient's server generates a bounce notification, it acts as a sender itself, attempting to deliver this notification back to the return-path (or Mail From) address of the original email. For this bounce notification to be successfully delivered, the recipient's server needs to look up the MX record for the return-path domain. If this MX record is missing, incorrect, or points to a non-responsive server, the bounce notification cannot be delivered.
The inability to receive these bounce messages has a direct and detrimental impact on your sender reputation. ISPs and other mail servers expect legitimate senders to properly handle bounces, as this indicates good list hygiene and responsible sending practices. If your domain appears unable to receive bounce notifications, it suggests a lack of proper setup, which can lead to higher spam classifications or outright blocking.
Furthermore, a missing or incorrect MX record for your sending domain can also contribute to emails being flagged as spam. Mailbox providers, including Google and Microsoft, consider a domain's ability to receive mail as a sign of its legitimacy. If your domain looks like a send-only domain because it lacks proper MX records, it can raise red flags and negatively affect your sender reputation.
Scenario 1: Correct MX records
Bounce handling: Bounce notifications are successfully returned to your designated bounce address (usually managed by your email service provider or ESP). This allows for accurate tracking of invalid or problematic email addresses.
Reputation impact: Receiving bounces indicates good email list hygiene, which is a positive signal for ISPs. Your domain is seen as legitimate and well-managed.
Deliverability: Higher likelihood of emails reaching the inbox, as your domain appears trustworthy to recipient servers.
Scenario 2: Incorrect or missing MX records
Bounce handling: Bounce notifications fail to reach your system. This means you're unaware of failed deliveries and cannot update your mailing lists, leading to continued sending to invalid addresses.
Reputation impact: Inability to receive bounce feedback is a strong negative signal. It suggests poor list hygiene and can result in your domain being added to internal blocklists, reducing your sender score.
Deliverability: Significantly reduced inbox placement as ISPs view your domain with suspicion, routing more of your mail to spam folders or outright rejecting it.
MX records and sender reputation
Sender reputation is a crucial factor that determines whether your emails land in the inbox or the spam folder. It's a score ISPs assign to your sending domain and IP address based on various metrics, including bounce rates, spam complaints, and engagement. While MX records don't directly influence all these factors, their correct configuration contributes significantly to a positive overall impression.
A properly configured MX record signals to recipient servers that your domain is set up correctly and capable of handling email, both incoming and outgoing. This operational transparency is a positive indicator that contributes to a higher Sender Score and overall sender reputation. Conversely, missing or misconfigured MX records can lead to emails bouncing back (if a sender checks your MX before sending), or, more commonly, to your bounce notifications failing. This makes it impossible to remove invalid addresses from your list.
Maintaining a clean email list by promptly removing hard-bouncing addresses is paramount for a strong reputation. If you're unable to receive bounce notifications due to MX record issues, you'll continue to send to invalid addresses. This sustained sending to non-existent recipients is a major red flag for ISPs, signaling poor list hygiene and potentially leading to your domain or IP being added to a blacklist (or blocklist).
Best practices for MX records and sender reputation
Verify configuration: Ensure your MX records are correctly set up and point to the right mail servers, especially for your bounce domain.
Monitor DNS propagation: After making changes, allow sufficient time for DNS records to propagate globally. This can take anywhere from a few minutes to several hours.
Align with ESP recommendations: Most Email Service Providers (ESPs) provide specific MX record configurations. Adhering to these ensures proper bounce handling and optimal deliverability.
Dedicated bounce domain: Use a dedicated subdomain (e.g., bounce.yourdomain.com) for handling bounces to isolate reputation issues from your main sending domain.
Why MX records are essential for deliverability
Setting up MX records correctly is a fundamental step in ensuring your emails are not only delivered but also that your sender reputation remains healthy. The primary purpose of an MX record is to tell other mail servers which server is responsible for receiving mail for a specific domain. While it doesn't directly influence your ability to send, it profoundly impacts how bounce messages are handled.
If a mail server receives an email and determines it cannot be delivered (e.g., the mailbox doesn't exist), it needs to send a non-delivery report (NDR) or bounce notification back to the sender. For this notification to reach you (or your ESP), the sending server looks up the MX record of the return-path domain. If this record is missing or incorrect, the bounce notification will fail, meaning you won't know about the delivery failure.
This lack of feedback is detrimental to your sender reputation because ISPs interpret continued sending to invalid addresses as poor list management or even malicious behavior. Therefore, ensuring your MX records are correctly configured, especially for your bounce domain, is a passive yet powerful way to bolster your sender reputation and improve overall email deliverability.
Views from the trenches
Best practices
Always ensure MX records for your sender and bounce domains are accurately configured.
Use dedicated subdomains for bounces, with MX records pointing to your ESP's bounce handlers.
Monitor DNS changes carefully, especially for MX records, to prevent unexpected deliverability issues.
Regularly review your bounce reports and remove invalid addresses to maintain list hygiene.
Common pitfalls
Forgetting to set MX records for bounce subdomains, leading to missed bounce notifications.
Pointing MX records to the wrong server, preventing bounce messages from being received.
Not updating MX records after migrating ESPs or making infrastructure changes.
Assuming MX records are only for incoming mail and not relevant for sender reputation.
Expert tips
If a client owns the envelope from domain, it's generally best practice for the MX records for the bounce subdomain to point to the ESP's systems to handle out-of-band bounces effectively.
Some providers may penalize senders who cannot receive out-of-band (OOB) bounce notifications.
Properly configured MX records indicate operational transparency, which contributes positively to your Sender Score.
The absence of a valid MX record for the Mail From domain can negatively affect your sender reputation, as it suggests an inability to receive feedback.
Expert view
An expert from Email Geeks says MX records do not directly cause hard or soft bounces, as bounces are often generated within the SMTP dialog. However, when a bounce generates an email, the sending server will look up the MX record for the return-path domain to deliver that bounce email. Your reputation will suffer if the from/SMTP from domain is unable to receive emails.
2023-08-01 - Email Geeks
Expert view
An expert from Email Geeks says vacation notices are not bounces themselves, but they are typically routed to the same destination as out-of-band bounce notifications.
2023-08-01 - Email Geeks
Final thoughts
MX records are more than just technical necessities; they are foundational to the trustworthiness and efficiency of your email operations. While they don't directly cause emails to bounce, their misconfiguration severely impairs your ability to receive critical bounce notifications.
This inability to process bounces leads to inflated bounce rates, poor list hygiene, and a damaged sender reputation, ultimately hindering your email deliverability. Regular checks and adherence to best practices for MX record configuration are not just advisable; they are essential for anyone serious about reaching the inbox consistently.
