Does a sending IP address need to accept incoming SMTP connections for email deliverability?

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 Checking for inbound connections on the sending IP is considered an outdated, irrelevant, or misguided practice.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  • Inbound Irrelevance: Checking for or requiring inbound SMTP connections on the sending IP address is considered an outdated or useless check by experienced email professionals and is not a factor in modern deliverability assessments.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
8Marketer 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.

November 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.

May 2024 - Reddit
Marketer view

Email marketer from SendGrid explains that deliverability depends on factors like sender reputation, authentication (SPF, DKIM, DMARC), and list hygiene. The ability to accept incoming SMTP connections on the sending IP is not listed as a requirement.

September 2022 - SendGrid
Marketer view

Email marketer from Quora explains that the sending IP doesn't need to accept incoming connections. What matters is the ability to send emails out and proper authentication.

January 2025 - Quora
Marketer view

Email marketer from Mailjet shares that the sending IP does not need to accept incoming SMTP connections. Mailjet handles the SMTP infrastructure. Users only need to configure their sending domain.

December 2022 - Mailjet
Marketer view

Email marketer from Reddit responds that focusing on the sending IP accepting incoming connections isn't relevant. Instead, ensure your domain has valid SPF, DKIM, and DMARC records.

March 2025 - Reddit
Marketer view

Email marketer from Email Geeks explains that checking if something can receive mail is done on the domain level, not IP. The IP you are sending mail from doesn’t necessarily need to receive stuff. Some might check if the domain they receive mail from can in fact receive email by checking the MX record.

February 2022 - Email Geeks
Marketer view

Email marketer from Neil Patel's Blog shares that while IP reputation is crucial for deliverability, whether an IP accepts incoming SMTP connections is not a direct factor. Focus should be on maintaining a good sending reputation through authentication and engagement.

August 2024 - Neil Patel's Blog

What the experts say
5Expert 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.

June 2021 - 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.

January 2023 - Email Geeks
Expert view

Expert from Email Geeks states that the check is actually if the domain has an MX record and the MX accepts mail, not the sending IP.

March 2023 - Email Geeks
Expert view

Expert from Word to the Wise responds that while reverse DNS is important for IP reputation, accepting inbound connections on port 25 is not usually a requirement for sending IP addresses to achieve good deliverability.

July 2023 - Word to the Wise
Expert view

Expert from Spam Resource explains that a properly configured outbound SMTP server primarily needs to establish connections to recipient mail servers. It doesn't require accepting inbound SMTP connections for deliverability.

March 2024 - Spam Resource

What the documentation says
3Technical 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.

October 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.

January 2023 - SparkPost
Technical article

Documentation from Microsoft Learn explains that SMTP servers typically do not require accepting incoming connections on port 25 for outbound email delivery. The primary function is to establish outbound connections to recipient mail servers.

May 2021 - Microsoft Learn