Summary
A broad consensus across experts, email marketers, and documentation indicates that a sending IP address does NOT need to accept incoming SMTP connections to achieve good email deliverability. The focus should be on domain-level checks (MX records), sender reputation, proper email authentication (SPF, DKIM, DMARC), outbound connectivity, and list hygiene. Checking for inbound connections on the sending IP is considered an outdated, irrelevant, or misguided practice.
Key findings
- Domain-Level Checks: Receiving mail servers primarily check the domain's MX records to verify mail acceptance, not the sending IP's ability to accept connections.
- Authentication is Key: Proper implementation and maintenance of SPF, DKIM, and DMARC are essential for verifying the sender's identity and improving deliverability.
- Sender Reputation Matters: A good sender reputation is crucial for deliverability and is built through authentication, engagement, and responsible sending practices.
- Outbound Connectivity: The sending server must be able to reliably initiate outbound connections to recipient mail servers. This is the primary function of an SMTP server.
- Inbound Irrelevance: Checking for or requiring inbound SMTP connections on the sending IP address is considered an outdated or useless check by experienced email professionals and is not a factor in modern deliverability assessments.
Key considerations
- Prioritize Authentication: Focus on setting up and diligently maintaining SPF, DKIM, and DMARC records for your sending domain to ensure proper email authentication.
- Build a Good Reputation: Adopt responsible email marketing practices (e.g., permission-based sending, list hygiene, engaging content) to build and maintain a positive sender reputation.
- Monitor Deliverability: Regularly monitor your IP and domain reputation and track email deliverability metrics to identify and address any potential issues.
- Optimize Outbound Configuration: Ensure that your SMTP server is properly configured for reliable outbound connections to recipient mail servers.
- Ignore Inbound Requirements: Do not prioritize or spend time troubleshooting issues related to accepting inbound SMTP connections on your sending IP address, as this is not a requirement for deliverability.
What email marketers say
8 marketer opinions
The consensus from email marketers and experts is that a sending IP address does not need to accept incoming SMTP connections for optimal email deliverability. Deliverability primarily relies on domain-level checks (MX records), sender reputation, proper email authentication (SPF, DKIM, DMARC), outbound connectivity, and list hygiene, rather than the ability of the sending IP to accept inbound connections.
Key opinions
- Domain-Level Checks: Email receivers focus on the domain's MX records to verify mail acceptance, not the sending IP's ability to accept connections.
- Sender Reputation: A good sender reputation is crucial for deliverability and is built through authentication and engagement.
- Authentication: Proper implementation of SPF, DKIM, and DMARC is essential for verifying the sender's identity and improving deliverability.
- Outbound Connectivity: The sending server must be able to initiate outbound connections to recipient mail servers.
- List Hygiene: Maintaining a clean and engaged email list is vital for a good sender reputation and high deliverability.
Key considerations
- Focus on Authentication: Prioritize setting up and maintaining SPF, DKIM, and DMARC records to authenticate your sending domain.
- Monitor Sender Reputation: Regularly monitor your IP and domain reputation to identify and address any issues affecting deliverability.
- Maintain List Hygiene: Implement processes to remove inactive or unengaged subscribers from your email list.
- Outbound SMTP: Ensure your SMTP server can reliably establish outbound connections to recipient mail servers.
Marketer view
Email marketer from Stack Overflow clarifies that outbound SMTP servers are not required to accept incoming SMTP connections. Focus should be on outbound connectivity and DNS records.
7 Feb 2022 - Stack Overflow
Marketer view
Email marketer from Reddit shares that a sending server does not need to accept incoming SMTP connections. The important aspect is that the server can initiate outgoing connections to other mail servers.
11 Dec 2024 - Reddit
What the experts say
5 expert opinions
Experts across various email platforms and resources largely agree that a sending IP address does *not* need to accept incoming SMTP connections for good email deliverability. The focus is instead on domain-level configurations like MX records, outbound connection capabilities, and a good sender reputation. Checking for inbound connections is considered an outdated or misguided practice by experienced professionals.
Key opinions
- MX Record Importance: The presence and functionality of a domain's MX record are the primary factors assessed by receiving mail servers, not the sending IP's ability to accept connections.
- Industry Consensus: Requiring inbound connections on port 25 is not a common or recommended practice within the email industry.
- Outdated Practice: Checking for inbound SMTP connections is considered a useless check by ISPs and experts with expertise in email deliverability.
- Reverse DNS is important: reverse DNS is important for IP reputation
Key considerations
- Focus on Outbound: Ensure your SMTP server is properly configured for outbound connections to recipient mail servers.
- Domain Configuration: Verify and maintain proper MX records for your sending domain.
- Sender Reputation: Prioritize building and maintaining a positive sender reputation through responsible email practices.
- Ignore Inbound: Do not be concerned with whether your sending IP address accepts inbound connections on port 25.
Expert view
Expert from Email Geeks says that this is the first she’s ever heard of requiring the sending IP to accept connections on port 25, and that they've been sending from an IP that doesn’t receive email for at least 5 years.
30 Aug 2022 - Email Geeks
Expert view
Expert from Email Geeks shares that only the tiniest misguided email domains are worried about connecting back to your IP on port 25, stating that any real ISP or anyone with expertise would know it’s a useless check.
8 Jun 2024 - Email Geeks
What the documentation says
3 technical articles
Email deliverability documentation consistently indicates that a sending IP address is *not* required to accept incoming SMTP connections. The focus is on outbound connections and proper configuration of email authentication protocols like SPF, DKIM, and DMARC. SMTP is inherently a push protocol where the sending server initiates the connection.
Key findings
- Outbound Focus: SMTP servers should primarily focus on establishing outbound connections to recipient mail servers.
- Push Protocol: SMTP operates as a push protocol, with the sending server initiating connections.
- Authentication Importance: Proper configuration of SPF, DKIM, and DMARC is critical for deliverability.
- Inbound Irrelevance: Accepting inbound connections on the sending IP is not a relevant requirement for deliverability.
Key considerations
- Outbound Configuration: Ensure your SMTP server is correctly configured to establish outbound connections.
- Implement Authentication: Prioritize the proper setup and maintenance of SPF, DKIM, and DMARC records for your sending domain.
- Refer to Documentation: Consult relevant documentation (e.g., RFCs, ESP documentation) for accurate configuration guidelines.
- Ignore Inbound: Do not prioritize or troubleshoot issues related to accepting inbound SMTP connections on the sending IP.
Technical article
Documentation from RFC Editor explains that SMTP is primarily a push protocol where the sending server initiates the connection to the receiving server. There is no requirement for the sending IP to accept incoming SMTP connections.
26 Dec 2023 - RFC Editor
Technical article
Documentation from SparkPost explains that the focus should be on configuring SPF, DKIM, and DMARC properly. Accepting inbound connections on the sending IP is not mentioned.
13 Oct 2022 - SparkPost
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