Proofpoint Postmaster

Proofpoint is an active participant in the global email ecosystem. Our postmaster represents Proofpoint customer interests with third party providers and is fluent in the latest techniques to ensure clean and prompt email traffic. This article outlines current best practices to assist in reputation management and block list avoidance.

Introduction

Proofpoint is a cybersecurity company specializing in helping organizations protect against advanced cybersecurity threats and compliance risks, which includes protecting customers from harmful emails.  To do so, Proofpoint's systems determine, in part, the trustworthiness (aka the reputation) of the IP address and / or domain from which emails are sent. Indicators that an IP or domain is sending spam or malicious content, or that the mail server is not from a legitimate company will impact the reputation and may result in delays and blocked messages.

This page offers best practices for ensuring legitimate emails are successfully delivered to Proofpoint customers. It explains why emails might be blocked or delayed but does not cover all possible email delivery problems.

What are the main reasons an IP address or domain might be blocked by Proofpoint, and how can I fix these issues?

 

Missing or incorrectly configured rDNS (reverse DNS)

A common reason for email delivery problems is a missing or wrong PTR (Pointer) record. This is also known as “reverse DNS.” It links an IP address to a domain name. Checking DNS helps verify if an email sender is legitimate. If an IP does not have a correct PTR record, or if the domain name does not match the sending domain, the IP or domain might be flagged as harmful.  Make sure your IP address has a valid PTR record that matches its domain name.

 

Authentication

Emails that are not authenticated often have delivery problems. Proper email authentication including SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) are required. SPF specifies which IP addresses can send emails on behalf of a domain. This prevents spoofing. DKIM adds a digital signature to verify email authenticity and prevent tampering.

To troubleshoot authentication related delivery problems, ensure that:

  • DNS records include a valid SPF record listing all authorized IP addresses
  • The DKIM record exists with a valid public key
  • The sending email server signs outgoing emails with the DKIM private key.

 

Outbound spam (intentional or unintentional)

Spam refers to unsolicited emails or other digital communications sent to an individual or group of recipients. This includes unsolicited commercial messages or malicious messages like phishing scams. When a spam filter identifies spam emails, the IP addresses or domains may be blocked, prohibiting the delivery of the messages. Some proactive steps you can take to avoid legitimate emails from being identified as spam or your IP and/or domain from being blocked due to the detection of malicious spam include:  

  • Ensure email best practices are followed
  • Secure internal systems against unauthorized use
  • Be compliant with Internet privacy laws
  • Authenticate your emails
  • Avoid using misleading subject lines
  • Send relevant content
  • Send emails to recipients who have opted in or requested communications.

 

Infected website / domain

If your website or domain is infected, emails linked to it will be blocked. Threat actors can exploit vulnerabilities in a website or device to spread spam or harmful content. This affects email delivery and your domain’s reputation. Protect against these threats by:

  • Regularly evaluating websites and internal networks for malware
  • Keep software and plugins updated
  • Implement robust security measures and detections.

If your domain is blocklisted, identify and remove the infection, then request delisting from blocklists to restore your email deliverability.

 

Additional pro-tips / Recommended sender best practices

 

New IPs

New IPs do not have a history. They are not trustworthy.  Emails sent from new IPs are often marked as spam. To help establish the IPs reputation and avoid having emails sent from the IPs blocked as spam, gradually increase email volume and ensure compliance with email best practices.

 

Use dedicated IPs

Dedicated IPS are better than shared IPs. Dedicated IP addresses can improve email deliverability by ensuring sending reputation is solely based on a controlled email source. With a dedicated IP, there is no risk of contamination from other sender's poor practices or delivery rates.

 

Do not send marketing from same IPs as user email

Avoid sending marketing emails from the same IPs used for transactional or user emails. Separating these helps maintain the reputation of your transactional IPs and ensure critical emails are delivered reliably.

 

Unsubscribe

Include a clear and easy-to-find unsubscribe option in all marketing emails. Providing a straightforward way for recipients to opt-out not only complies with legal requirements but will also help maintain a healthy sender reputation by reducing spam complaints and scrubbing email lists.

 

Keep lists clean

Maintaining good list hygiene is crucial for email deliverability. The regular scrubbing of email lists by removing inactive, invalid, or unengaged addresses reduces bounce rates and spam complaints, and ensures emails reach an engaged and interested audience.

 

Pay attention to error messages

Mail logs can show why emails are not delivered. Common errors can indicate issues such as authentication failures, blocklisting, or content-related problems, allowing focused troubleshooting and resolution of delivery issues.

 

Other useful information

 

Proofpoint’s mail delivery error messages and what they mean

 

Additional Resources:

Business guide for Federal CAN-SPAM compliance:
https://www.ftc.gov/business-guidance/resources/can-spam-act-compliance-guide-business

Canada's anti-spam legislation:
https://ised-isde.canada.ca/site/canada-anti-spam-legislation/en

M3AAWG Sender Best Common Practices:
https://www.m3aawg.org/sites/default/files/document/M3AAWG_Senders_BCP_Ver3-2015-02.pdf

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Last updated September 25, 2024.