Why is Virgin Media bouncing emails with 'Header From domain is invalid' error, and how to fix it?
Michael Ko
Co-founder & CEO, Suped
Published 23 May 2025
Updated 18 Aug 2025
7 min read
Recently, some email senders have encountered a frustrating bounce message from Virgin Media. The error, "421 4.2.0 MXIN619 Your Header From domain is invalid", indicates an issue with the sending domain's configuration, preventing your emails from reaching recipients on their network. This can be particularly puzzling when previous checks showed no problems.
This sudden change suggests a stricter policy by Virgin Media regarding how they validate sender domains. It's a common move by internet service providers (ISPs) to combat spam and phishing, but it means senders need to ensure their DNS records are meticulously set up. Getting ahead of these changes is crucial for email deliverability.
Understanding the error: 'Header From domain is invalid'
The error message, "Header From domain is invalid", directly points to a problem with the domain specified in the From header of your email. While it might seem vague, it usually signifies that Virgin Media could not properly resolve or validate this domain during the email transaction. This often stems from missing or improperly configured DNS records like MX or A records.
Historically, some smaller domains or those used solely for sending emails might not have had complete DNS setups, especially if they weren't used to receive mail. However, Virgin Media's recent policy adjustment means they are now performing more stringent checks. This change aims to verify the legitimacy of the sending domain and the sender's identity, thereby reducing the volume of illegitimate email. This is a common practice among major mail providers.
It is important to remember that even if your domain isn't intended to receive emails, the presence of appropriate DNS records is still critical for email deliverability. Mail servers (including Virgin Media's) often perform reverse DNS lookups or check for basic records like MX and A records as part of their anti-spam checks. If these are missing, it can flag your domain as suspicious or invalid.
Virgin Media's strict validation
Virgin Media has implemented a more rigorous validation process for incoming emails. This includes verifying that the sending domain's DNS records are properly configured, even for domains not typically used for receiving email.
The "Header From domain is invalid" error is a direct consequence of this tightened policy. It implies that their mail servers cannot find the expected DNS entries for your email's sending domain.
The critical role of DNS records
At the heart of this issue are missing or misconfigured DNS records, specifically MX and A records. While MX (Mail Exchanger) records are primarily for directing incoming mail, their presence, along with A (Address) records, serves as a strong indicator of a legitimate and actively managed domain. Some ISPs use the absence of these records as a heuristic to identify potentially spoofed or illegitimate senders.
For domains that send emails but don't receive them (e.g., dedicated sending subdomains), it was once common to omit MX records. However, with stricter anti-spam measures, this practice is becoming increasingly problematic. The presence of at least an A record, resolving to a valid IP address, and ideally an MX record, even if it points to a null MX, demonstrates that the domain is properly registered and has a legitimate purpose. This helps mail servers like Virgin Media's confirm the domain's validity.
Furthermore, if you are using a "cousin domain" like emails-yourdomain.com instead of your primary domain yourdomain.com, it can raise red flags. While technically permissible, these domains are often associated with less reputable sending practices. ISPs prefer that senders use their primary, well-established domains for email communication.
Domain with proper DNS
Trustworthy: Presence of MX and A records signals a legitimate, managed domain to ISPs.
Deliverability: Higher likelihood of emails being accepted and delivered to the inbox.
Standard Compliance: Aligns with modern email security best practices and RFC standards.
Domain with missing DNS
Suspicion: Absence of key DNS records raises red flags for spam filters, leading to bounces.
Rejection: Emails are likely to be rejected with errors like "Header From domain is invalid."
Reputation Impact: Can negatively affect your sending domain's overall reputation and cause blocklisting (or blacklisting).
Beyond DNS: DMARC and domain reputation
While MX and A records address the immediate Virgin Media bounce, a robust email security posture goes further. Implementing DMARC (Domain-based Message Authentication, Reporting, and Conformance) is no longer optional, especially with Google and Yahoo requiring it for bulk senders. DMARC builds upon SPF and DKIM to prevent email spoofing and phishing attacks by allowing domain owners to specify how receiving mail servers should handle emails that fail authentication.
A good domain reputation is paramount for consistent email delivery. Even if your DNS records are correct, a poor reputation can lead to emails being sent to spam folders or outright rejected. This reputation is influenced by factors such as bounce rates, spam complaint rates, email authentication, and whether your domain or IP address is on any blocklists (or blacklists).
Legacy configurations, especially those using separate send-only domains without comprehensive DNS records, are increasingly vulnerable to these stricter policies. Updating these configurations is no longer a suggestion, but a necessity to maintain deliverability and avoid future issues with other ISPs.
The p=none policy in this example allows you to monitor your email traffic and authentication results without affecting deliverability. It's a crucial first step before moving to more restrictive policies like p=quarantine or p=reject.
Step-by-step solutions to fix the issue
To resolve Virgin Media's "Header From domain is invalid" error and prevent similar issues with other ISPs, your primary focus should be on ensuring your sending domain has the correct and complete DNS records. This is especially true for any subdomains or cousin domains you use for email sending.
First, verify that your sending domain has both an MX record and an A record. Even if you don't receive emails on this domain, having these records in place provides necessary validation for receiving mail servers. For the MX record, you can point it to a null MX if no mail server exists to handle incoming mail for that domain. Additionally, ensure your SPF and DKIM records are correctly configured for all your sending sources.
Once your foundational DNS records are in order, turn your attention to DMARC. Start with a p=none policy to collect reports and understand your email ecosystem before moving to quarantine or reject policies. Regular monitoring of these reports will help you identify any authentication failures and promptly address them, ensuring continuous compliance with evolving ISP requirements and improving your overall deliverability rates.
DNS record checklist for email sending domains
A record: Ensure your sending domain (or subdomain) has an A record pointing to a valid IP address. This helps resolve the domain name to an IP.
MX record: Even if you don't receive mail, add an MX record. You can use a null MX (e.g., 0 example.com) if no mail server exists.
SPF record: Authorize all your sending IPs and third-party senders in your SPF record.
DKIM record: Ensure your DKIM records are correctly published and valid for all sending platforms.
DMARC record: Implement a DMARC record, starting with p=none for monitoring before enforcing policy.
Views from the trenches
When facing deliverability challenges, especially with specific ISPs like Virgin Media, it's beneficial to hear what others in the email community have experienced and how they resolved similar issues.
From recent discussions, it seems that the "Header From domain is invalid" error from Virgin Media is indeed a symptom of recent policy changes requiring more complete DNS setups, even for domains that don't receive emails. It reinforces the importance of proactive email hygiene and adapting to evolving sender requirements.
Best practices
Ensure all sending domains, including subdomains or 'cousin domains', have proper MX and A records configured.
Always implement SPF, DKIM, and DMARC for comprehensive email authentication, even for legacy clients.
Regularly monitor your DMARC reports to catch authentication failures early and maintain a healthy sending reputation.
Common pitfalls
Ignoring the absence of MX or A records for send-only domains, leading to rejections by stricter ISPs.
Using 'cousin domains' without robust authentication, which can raise suspicion with spam filters.
Delaying DMARC implementation, making it harder to diagnose authentication issues when they arise.
Expert tips
Always include an A record for both the visible From domain and the Return-Path subdomain in your DNS template to prevent issues with specific ISPs.
Even if a domain isn't meant to receive mail, adding a null MX record can satisfy checks by some mail servers.
The error message might be misleading; focus on fundamental DNS records like MX and A, alongside DMARC, as the root cause.
Expert view
Expert from Email Geeks says there was no MX or A record for the sending domain, emails-purecollection.com.
2025-02-17 - Email Geeks
Expert view
Expert from Email Geeks says Virgin Media likely changed their policy and is no longer accepting mail from senders without MX records.
2025-02-17 - Email Geeks
Ensuring email deliverability resilience
Dealing with bounce messages like "Header From domain is invalid" from Virgin Media requires a proactive and thorough approach to your email infrastructure. The core of the problem often lies in incomplete or missing DNS records for your sending domains.
By ensuring that every domain you send from, including subdomains and cousin domains, has proper MX, A, SPF, DKIM, and DMARC records, you not only resolve current Virgin Media bounces but also fortify your email deliverability against future ISP policy changes. Embracing these best practices is essential for maintaining a strong sender reputation and ensuring your messages consistently reach the inbox.
Virgin Media. The error, "421 4.2.0 MXIN619 Your Header From domain is invalid", indicates an issue with the sending domain's configuration, preventing your emails from reaching recipients on their network. This can be particularly puzzling when previous checks showed no problems.
Google and 
Yahoo requiring it for bulk senders. DMARC builds upon SPF and DKIM to prevent email spoofing and phishing attacks by allowing domain owners to specify how receiving mail servers should handle emails that fail authentication.
