What is the difference between smtpd_tls and smtp_tls in Postfix?

The smtpd_tls_* parameters configure TLS for emails your Postfix server *receives*. The smtp_tls_* parameters configure TLS for emails your Postfix server *sends* to other mail servers. For GPT reporting, you need to focus on smtp_tls_ settings.

Why does Google Postmaster Tools show lower TLS encryption rates than expected?

GPT's TLS reporting reflects the percentage of incoming traffic to Gmail that was encrypted. Discrepancies can occur if your Postfix server sometimes falls back to unencrypted connections (e.g., if smtp_tls_security_level is set to may ), or due to temporary network issues, certificate problems, or Google's data processing. It's an aggregate view, so even a small number of unencrypted connections can affect the percentage.

How can I get more detailed TLS logging in Postfix?

You can increase the verbosity of your Postfix logs by setting smtp_tls_loglevel = 2 or higher in your main.cf file. This will provide more detailed information about the TLS handshake process, including cipher negotiation and certificate issues, in your mail logs (e.g., /var/log/mail.log or /var/log/maillog ).

What are the common causes of Postfix TLS encryption failures?

Common causes include expired or misconfigured SSL/TLS certificates, incorrect smtp_tls_security_level settings (e.g., using may ), outdated Postfix or OpenSSL versions lacking support for modern cipher suites, and firewall rules blocking TLS negotiation ports. Checking these areas systematically is key.

Is there a direct way to contact Google about Postmaster Tools discrepancies?

While Postmaster Tools provides insights into authentication and encryption, it's not designed for real-time contact with their support team. For severe deliverability issues, ensure your email authentication (SPF, DKIM, DMARC) is robust. You can explore DMARC reports from Google and Yahoo , which can offer additional data on TLS failures if configured to do so, providing another avenue for investigation.

How to troubleshoot Postfix TLS encryption issues and GPT reporting discrepancies? - Troubleshooting - Email deliverability - Knowledge base

Dealing with inconsistencies in email delivery and reporting can be incredibly frustrating. One common scenario involves seeing a dip in your TLS encryption rates within Google Postmaster Tools (GPT), especially after making changes like adding new Postfix servers. While your own logs and email headers might indicate successful TLS encryption, GPT's data tells a different story.

This discrepancy can be particularly confusing because it directly impacts your understanding of email security and deliverability. It's not uncommon to find that even with identical configurations between old and new servers, a new host might inexplicably lead to these reporting issues while others on the same infrastructure remain unaffected.

My aim here is to help you navigate this complex situation, identifying the root causes of Postfix TLS problems and understanding why Google Postmaster Tools might be showing data that doesn't quite align with your expectations. We will explore key configuration settings, logging strategies, and how GPT interprets email traffic.

Understanding Postfix TLS configuration

When troubleshooting Postfix TLS encryption issues, a crucial first step is to carefully examine your Postfix configuration, particularly the main.cf file. It's easy to confuse settings for incoming versus outgoing TLS. The smtpd_tls_ parameters control TLS for incoming email to your Postfix server, while smtp_tls_ parameters govern TLS for outgoing emails that your server sends to others, like

Gmail. If you're seeing discrepancies in GPT, it's likely an issue with your outgoing TLS configuration.

A common setting to check is smtp_tls_security_level. Setting this to may generally means Postfix will attempt to use TLS, but will proceed without it if the remote server doesn't support it or if the handshake fails. This can lead to unencrypted connections that GPT will flag. For more detailed guidance, the Postfix documentation on client TLS levels is an excellent resource.

Incoming TLS (SMTPD)

Purpose: Handles encryption for emails being received by your Postfix server.
Parameters: Configuration settings typically start with smtpd_tls_, such as smtpd_tls_cert_file and smtpd_tls_key_file.
Logging: Monitored via smtpd_tls_loglevel, which affects how much detail is written to your logs regarding incoming TLS sessions.

Outgoing TLS (SMTP)

Purpose: Manages encryption for emails sent from your Postfix server to other mail servers.
Parameters: Settings that start with smtp_tls_, such as smtp_tls_security_level.
Logging: Use smtp_tls_loglevel to get details on outgoing TLS connections.

Decoding Google Postmaster Tools data

Even with correct Postfix TLS settings, Google Postmaster Tools (GPT) might show discrepancies. This often stems from how GPT processes data. It measures encryption across all traffic it receives from your domain, not just individual messages. So, if a small percentage of connections somehow fall back to unencrypted delivery, even if most emails go through encrypted, it can cause the overall encryption rate to drop significantly.

One factor to consider is that GPT data can sometimes be glitchy and inconsistent. It's not always a real-time, perfect reflection of your traffic. During periods like IP warmup for new servers, traffic patterns can be erratic, which might further contribute to what looks like a drop in encryption when it's really just a minor fluctuation in a specific subset of connections. I often see incorrect SPF and DKIM authentication rates too, further indicating that GPT isn't always 100% accurate.

Additionally, GPT's reporting might not distinguish between full TLS encryption and partial or opportunistic TLS. If your Postfix server establishes a connection that doesn't fully meet Google's strict TLS requirements, even if it uses STARTTLS, it might still be counted against your overall encryption rate. This is particularly relevant if you're seeing TLS errors when sending to Gmail or Google STARTTLS errors that lead to reduced send rates.

Common TLS pitfalls and solutions

Several common pitfalls can lead to TLS encryption issues in Postfix. First, ensure your certificates are correctly installed and valid. An expired or incorrectly configured certificate is a frequent culprit. You should verify that your smtpd_tls_key_file, smtpd_tls_cert_file, and smtpd_tls_CAfile paths point to the correct and readable files on your server. If you encounter SSL/TLS key size errors, this also indicates a certificate problem.

Another common issue is an outdated Postfix version or OpenSSL library. Older versions might not support the latest TLS protocols and cipher suites, leading to handshake failures with modern mail servers. I've also seen Postfix TLS handshake failures when connecting to an Exchange server due to protocol mismatches, even if the general configuration seemed fine. Regularly updating your system ensures compatibility and security.

Firewall rules can also silently interfere with TLS. While port 25 or 587 might be open, specific firewall configurations could block the dynamic ports used for TLS negotiation or certificate validation. Always review your firewall settings on the new servers to ensure they are not inadvertently blocking secure connections. This is particularly important for servers that are under IP warmup, as new network paths might be subject to different security policies.

Here’s a table summarizing common smtp_tls_security_level settings and their implications:

Setting	Description	Impact on TLS
none	No TLS is used for outgoing connections.	Emails sent unencrypted. Very poor for deliverability and reputation.
may	Opportunistic TLS. Postfix attempts TLS but proceeds without it if unavailable or if there's a handshake failure.	Some emails may be sent unencrypted, leading to GPT discrepancies. Not ideal for sensitive mail.
encrypt	Mandatory TLS. Requires encryption but does not perform certificate verification.	Ensures encryption, but still vulnerable to man-in-the-middle attacks if certificates are not verified. Improves GPT score.
verify	Mandatory TLS with certificate verification. Requires the server certificate to be valid and trusted.	Highest security. Email delivery fails if TLS or certificate verification fails. Best for sensitive data. Maximizes GPT score.

Advanced troubleshooting techniques

To get to the bottom of persistent TLS issues, you might need to employ advanced troubleshooting techniques. Enabling higher smtp_tls_loglevel (e.g., 2 or higher for more verbose output) can provide critical insights into TLS handshake processes in your Postfix logs. This will show you exactly what happens during a TLS negotiation, including certificate exchanges, protocol versions, and cipher suites used, which can pinpoint the exact point of failure.

Set Postfix outgoing TLS log levelshell

smtp_tls_loglevel = 2

Consider implementing MTA-STS (Mail Transfer Agent Strict Transport Security). While not a direct fix for existing TLS issues, MTA-STS can enforce mandatory TLS for connections to supporting domains. If your emails fail to deliver with MTA-STS, it’s a strong indicator of a TLS configuration problem that needs immediate attention, as all unencrypted or improperly encrypted connections would be rejected outright, preventing delivery altogether rather than simply reporting a low TLS rate in GPT.

Views from the trenches

Best practices

Ensure your Postfix and OpenSSL versions are up-to-date to support modern TLS protocols and cipher suites.

Always set `smtp_tls_security_level = verify` for outgoing mail to ensure full encryption and certificate validation, improving deliverability.

Regularly monitor your Postfix logs with increased `smtp_tls_loglevel` during troubleshooting phases.

Verify that your DNS records, including those for SPF and DKIM, are correctly configured.

Common pitfalls

Confusing `smtpd_tls_` (incoming) with `smtp_tls_` (outgoing) settings in Postfix configuration.

Using `smtp_tls_security_level = may` or `none`, which allows unencrypted fallback and leads to GPT discrepancies.

Overlooking firewall rules that might silently block TLS negotiation on new servers or specific ports.

Assuming successful email header encryption guarantees 100% TLS rate in GPT.

Expert tips

Use external tools to test your SMTP server's TLS capabilities from different locations.

If warming up new IPs, ensure TLS configurations are identical and thoroughly tested before scaling traffic.

Pay close attention to certificate chain issues, as a missing intermediate certificate can cause failures.

Remember that GPT aggregates data, so a small number of unencrypted connections can skew overall percentages.

Expert view

Expert from Email Geeks says Postfix does not log TLS sessions by default unless in debug mode, so check if you have asked other Mailbox Providers if they can check their TLS event data for your IPs or domains.

2024-01-09 - Email Geeks

Marketer view

Marketer from Email Geeks says that a similar problem occurred last year with a different product where debug mode logs did not show any connections to Gmail with TLS not applied or failing.

2024-01-09 - Email Geeks

Summary of troubleshooting steps

Troubleshooting Postfix TLS encryption issues and GPT reporting discrepancies requires a methodical approach. It involves dissecting your Postfix configuration, especially the subtle differences between incoming and outgoing TLS settings, and understanding the nuances of how platforms like Google Postmaster Tools collect and present data.

By meticulously reviewing logs, ensuring correct TLS security levels, and being aware of factors like IP warmup affecting data, you can diagnose and resolve these issues. Maintaining a robust and correctly configured TLS setup is crucial for your email security and to ensure your messages reach the inbox with the expected level of encryption.