How to troubleshoot Postfix TLS encryption issues and GPT reporting discrepancies?

Marketer from Email Geeks suggests checking for unrecognized IPs in the IP reputation dashboard, noting that dramatic drops in TLS can be a sign of DKIM replay attacks.

Email marketer from StackExchange recommends ensuring that STARTTLS is properly advertised and negotiated during the SMTP handshake. States you can test using `swaks --server your.server.com --port 587 --starttls`.

Email marketer from ServerFault explains Opportunistic TLS isn't always guaranteed if the receiving end doesn't support TLS. States you should use DANE and DNSSEC

Email marketer from MXToolbox suggests using their online tools to check for SMTP connectivity issues, DNS record problems, and blacklist status, which can indirectly affect TLS reporting.

Email marketer from Reddit suggests checking the Postfix configuration files (`main.cf` and `master.cf`) for any conflicting or misconfigured TLS parameters, and ensuring the certificate and key files are correctly specified and accessible.

Email marketer from Reddit suggests checking SPF, DKIM, and DMARC records to ensure proper authentication and improve email deliverability, which can influence how Gmail perceives TLS encryption.

Email marketer from EmailSecurityBlog.com explains that checking that you have a valid SSL certificate and that it hasn't expired is very important for TLS.

Marketer from Email Geeks recommends checking and configuring the `smtp_tls_loglevel` and `smtp_tls_security_level` in the Postfix configuration to ensure proper TLS settings for outgoing email. Provides a link to the postfix documentation to aid in debugging.

Marketer from Email Geeks suggests checking if Postfix logs TLS sessions by default and recommends asking another Mailbox Provider (MBP) to check their TLS event data for the same IPs or domains.

Email marketer from ServerFault suggests verifying the TLS version and cipher suites supported by both the Postfix server and the receiving server using `openssl s_client`. Also make sure the receiving end is also configured correctly.

Expert from Word to the Wise explains that DANE can be used to ensure that TLS is used. DANE uses DNSSEC which can be configured in your DNS to secure the authentication.

Expert from Spam Resource explains that if you are having issues with DMARC failures with messages that should have TLS, check you are configuring your mail server correctly. Ensure the message is sent via TLS and the connecting IP is correct.

Documentation from Google explains the importance of SPF, DKIM, and DMARC records and how they impact email authentication and deliverability to Gmail accounts. Also explains TLS and its importance for email transit.

Documentation from OpenSSL explains how to use the `openssl s_client` command to test TLS connections, verify certificate validity, and check the negotiated cipher suite.

Documentation from Postfix.org explains that proper TLS configuration involves setting `smtp_tls_security_level` to `may` or `encrypt` in the `main.cf` file, and that logging can be enabled using `smtp_tls_loglevel` to diagnose issues.