SSL Certificate Verification Failed: Self-signed Certificate¶

In professional email server configurations, an SSL Certificate Verification Failed error is a critical issue. If your tool.tl diagnostics show [SSL: CERTIFICATE_VERIFY_FAILED], it usually means your server is using a self-signed certificate.

Why Self-signed Certificates are a Problem¶

A self-signed certificate is generated by you and is not signed by a trusted Certificate Authority (CA). While it encrypts the connection, it cannot prove your identity. * Rejection Risk: Major providers like Gmail and Outlook may reject your emails or flag them as spam if the TLS certificate is untrusted. * Security Warnings: Mail clients (Outlook, iOS Mail, etc.) will display scary security warnings to users.

The Solution: Use a Trusted SSL Certificate¶

1. Use Let's Encrypt (Recommended)¶

This is the most popular, free, and automated solution. Use certbot to issue a certificate for your mail domain (e.g., mail.yourdomain.com).

# For Ubuntu and Standalone mode
sudo apt update
sudo apt install certbot
sudo certbot certonly --standalone -d mail.yourdomain.com

2. Update Dovecot/Postfix Configuration¶

Once issued, point your config files to the new .pem files:

Postfix (/etc/postfix/main.cf):

smtpd_tls_cert_file=/etc/letsencrypt/live/mail.yourdomain.com/fullchain.pem
smtpd_tls_key_file=/etc/letsencrypt/live/mail.yourdomain.com/privkey.pem

Dovecot (/etc/dovecot/conf.d/10-ssl.conf):

ssl_cert = </etc/letsencrypt/live/mail.yourdomain.com/fullchain.pem
ssl_key = </etc/letsencrypt/live/mail.yourdomain.com/privkey.pem

Next Steps¶

Deploy a trusted CA certificate.
Restart Postfix and Dovecot.
Go to the Email Diagnostics Tool for testing.

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