When delving into the intricacies of email deliverability, one common question that arises is whether an A record is truly necessary for your email sending domains. An A record, or address record, is a fundamental DNS record that maps a domain name to an IPv4 address. It tells the internet where to find your website or other services associated with that domain.
For email, we typically think of MX records as the primary DNS record for mail exchange, directing incoming mail to the correct servers. However, the role of an A record for domains that send emails can be a bit more nuanced than for domains that primarily receive mail or host websites.
While an A record isn't strictly mandated by RFC standards for a sending domain, its presence, or lack thereof, can significantly influence how your emails are perceived by recipient mail servers. This ultimately impacts your inbox placement and overall email deliverability. Let's explore why this is the case and what best practices suggest.
Understanding this distinction is crucial for maintaining a strong sender reputation and avoiding common pitfalls that lead to emails landing in spam folders or being outright rejected. We'll look at the technical requirements versus recommended best practices to provide a clearer picture.
The fundamental role of A records in DNS
An A record is essentially the foundational element of DNS. It directly connects your human-readable domain name, such as example.com, to a numerical IP address, like 192.0.2.1. This mapping is vital for web browsers to locate and display websites. Without an A record, a domain simply wouldn't resolve on the internet.
For email, the primary record for directing mail to your server is the MX record. An MX record specifies which mail servers are responsible for accepting email on behalf of your domain. For an MX record to function correctly, it must point to a hostname that has an associated A (or AAAA for IPv6) record. This is why you need an A record for your mail server, even if it's not the same as your sending domain.
The confusion often arises because the domain you use in your "From" header (Header From) for sending emails might be different from the domain used in the "MAIL FROM" (Envelope From or Return-Path) address, which is typically the one checked by SPF. Both of these can influence deliverability differently. For more on this, you can learn about A records for return-path domains.
While a domain technically could send email with just an MX record (though this is primarily for receiving mail), modern email systems rely on a broader set of DNS records, including SPF, DKIM, and DMARC, for authentication and security. These records help recipient servers verify the legitimacy of incoming emails and protect against spoofing and phishing.
Impact on deliverability and sender reputation
When sending emails, your mail server's IP address needs to be resolvable. This is typically handled by a PTR record (reverse DNS), which maps an IP address back to a hostname. However, the sending domain itself, particularly the domain in the Header From address, also plays a role in sender reputation and trust.
While an A record for the Header From domain isn't explicitly required for the email to be sent, it's widely considered a best practice. This is because many recipient servers and spam filters perform various checks on the sending domain to assess its legitimacy. A domain without a valid A record can appear suspicious, akin to a physical address that doesn't exist.
This becomes even more relevant with new sender requirements from major mailbox providers. For instance, Google and Yahoo now require valid forward and reverse DNS records for sending IPs and domains. While this primarily refers to the sending IP having a PTR record and that PTR record's hostname having an A record, it underscores the general expectation of proper DNS configuration across the board for all elements involved in email sending.
A general rule of thumb is that if a domain is used in any part of the email header or envelope, it should be a real, resolvable domain. This transparency contributes positively to your domain reputation.
Why it's a best practice
Technical necessity
MX record dependency: An A record is technically only required for the hostname pointed to by the MX record, not necessarily the email sending domain itself, if the primary goal is just sending.
RFC compliance: The RFCs primarily specify MX records for email reception. For sending, the IP needs a PTR record, and that PTR needs a corresponding A record.
While an A record might not be a direct technical requirement for the Header From domain to send an email, not having one can lead to deliverability issues. Receiving mail servers often perform DNS lookups on various parts of an email, including the domain used in the "From" header. If this lookup fails, or if the domain doesn't resolve to a valid IP address, it can raise a red flag.
This is where the concept of a domain appearing "suspicious" comes into play. A domain that is actively sending emails but has no public A record (or is unreachable) can be interpreted as potentially malicious or poorly configured. This can contribute to your emails being marked as spam or even triggering a blocklist (or blacklist) listing.
Additionally, many email authentication mechanisms, while not directly dependent on the A record of the Header From domain, benefit from a fully configured DNS setup. For example, a DMARC record helps define how receiving servers should handle emails that fail SPF or DKIM checks, and having a well-rounded DNS profile simply adds to the perceived trustworthiness of your sending domain.
While it's possible to send email from a domain that lacks a website, the presence of a resolvable A record for the sending domain, even if it just points to an informational page or redirects, signals legitimacy. The absence of a website doesn't inherently harm deliverability, but a non-resolvable domain does.
Recommended configurations and best practices
The bare minimum
IP resolves to a hostname: The sending IP address must have a valid PTR record that resolves to a hostname. Yahoo's best practices highlight this.
Hostname resolves to IP: That hostname must then have a corresponding A record that resolves back to the sending IP. This is often called a valid forward and reverse DNS setup.
Mail From domain: The MAIL FROM (Return-Path) domain should have an A record or MX record if it is to receive bounces or replies, which is often crucial for list hygiene.
Optimizing for deliverability
Header From domain: It is highly recommended that the Header From domain also has a public A record. This enhances perceived legitimacy and aids in positive sender reputation. Best practices for choosing an email sending domain emphasize this.
Web presence: If the A record for the sending domain points to a web server, ensure there's some content, even a simple redirect, to avoid a broken link when recipients investigate.
For the Mail From (or Envelope From) domain, having an A record is often more critical than for the Header From. Some Mail Transfer Agents (MTAs) may outright reject emails if the Mail From domain lacks a resolvable A record. This is a common stricter check, as the Mail From domain is central to the SMTP transaction and SPF authentication.
Here's an example of how you might configure a simple A record for a sending subdomain, pointing it to your primary website's IP or a dedicated landing page for email inquiries:
Example A record for sending subdomainDNS
Host: mail.yourdomain.com
Type: A
Value: 192.0.2.10
This setup allows recipient servers to perform a quick lookup, confirming that the domain exists and is associated with a legitimate IP, even if that IP doesn't directly send mail itself.
Summary of DNS records and their impact on email
DNS record type
Primary function for email
Impact on deliverability if missing
A record
Maps domain/hostname to IP address (e.g., for web presence or Mail From domain resolution).
Can lead to rejection if Mail From domain lacks an A record. Perceived as suspicious for Header From domains.
MX record
Directs incoming email to mail servers. While primarily for receiving, its absence on a sending domain can be a flag.
Maps an IP address back to a hostname (reverse DNS). Essential for email server identification.
Likely rejection or high spam classification rates, especially by major providers like Google and Yahoo.
SPF record
Authorizes sending IPs for a domain, preventing spoofing.
High risk of emails being marked as spam or rejected.
DKIM record
Digitally signs emails, verifying content integrity and sender identity.
Lower deliverability, increased spam classification risk due to lack of trusted authentication.
DMARC record
Policy for handling emails that fail SPF or DKIM alignment, provides reporting.
No policy for non-aligned mail, higher risk of spoofing and spam classification without enforcement.
While the absence of an A record for your Header From domain might not always result in an immediate email rejection, it does make your domain look less legitimate in the eyes of many email providers. This can negatively impact your sender reputation over time.
A domain with a complete and accurate DNS setup, including a resolvable A record for its sending domains and associated IPs, signals trustworthiness. This holistic approach to DNS configuration is a cornerstone of robust email deliverability and helps ensure your messages reach the inbox, rather than being diverted to the spam folder or blocked by a blocklist (or blacklist).
Views from the trenches
Best practices
Ensure a valid A record exists for your Mail From domain to prevent outright rejections by some MTAs.
Always have a resolvable A record for your sending domain, especially the Header From domain, to enhance perceived legitimacy.
Verify that your sending IP has a correct PTR record, and that PTR record resolves back to a hostname with an A record.
Configure a simple web page or redirect for your sending domain's A record to provide transparency to recipients.
Common pitfalls
Missing A records for Mail From domains, leading to rejections from strict receiving servers.
Neglecting to set up an A record for the Header From domain, causing suspicion among spam filters.
Incorrectly configured PTR records for sending IPs, which results in deliverability failures.
Not aligning the domain in the PTR record with the sending domain, reducing trust signals.
Expert tips
Implement a DMARC policy even at `p=none` to gain visibility into your email ecosystem and identify potential issues.
Regularly monitor your domain's DNS records to ensure they are correctly configured and updated.
Utilize subdomains for different types of email (e.g., marketing.example.com, transactional.example.com) to isolate reputation.
Test your email setup using online tools to verify DNS records and authentication passes before major sends.
Marketer view
A marketer from Email Geeks says it seems to be a standard best practice to add an A record for the subdomain used in the 5322 From header, often pointing to the client's website IP.
2019-07-12 - Email Geeks
Expert view
An expert from Email Geeks says an A record is essential for the MAIL FROM domain, while it's recommended but less critical for the Header From domain. Any domain without an A record can appear suspicious.
2019-07-12 - Email Geeks
Final thoughts on email sending domains
In conclusion, while an A record might not always be a strict technical prerequisite for an email sending domain, its presence is a significant best practice that profoundly impacts your email deliverability and sender reputation. The DNS landscape for email is complex, with multiple record types working in concert to establish trust and ensure messages reach their intended recipients.
Ensuring that your Mail From domain, Header From domain, and sending IPs all have correctly configured A and PTR records, alongside robust SPF, DKIM, and DMARC authentication, is vital for navigating the evolving landscape of email security and preventing your emails from being flagged as suspicious or ending up on a blocklist (or blacklist).
Investing time in a comprehensive DNS setup for your email infrastructure is not merely about meeting technical specifications, it's about building and maintaining the credibility of your sending domain, which is paramount for successful email campaigns and reliable communication.
Google and 
Yahoo.
