SMTP Error 101 occurs when there is a configuration issue with your SMTP settings. This error is commonly associated with Google SMTP and is often triggered by invalid SSL or TLS configurations.

What's Causing This SMTP Error 101:

The SMTP 101 error may be caused by:

• Misconfigured port.
• Invalid SMTP host server.
• Invalid SMTP IP address.
• Invalid use of SSL or TLS.

However, it is noteworthy that this error frequently occurs with Google SMTP due to issues related to SSL or TLS configurations.

How SMTP Error 101 Manifests in Different Environments:

SMTP Error 101 in phpmailer:

1. Case 1: "SMTP Error 101 - Misconfigured port in phpmailer."
2. Case 2: "SMTP Error 101 - Invalid SMTP host server in phpmailer."
3. Case 3: "SMTP Error 101 - Invalid SMTP IP address in phpmailer."
4. Case 4: "SMTP Error 101 - Invalid SSL or TLS usage in phpmailer."

SMTP Error 101 in Jenkins:

1. Case 1: "SMTP Error 101 - Misconfigured port in Jenkins."
2. Case 2: "SMTP Error 101 - Invalid SMTP host server in Jenkins."
3. Case 3: "SMTP Error 101 - Invalid SMTP IP address in Jenkins."
4. Case 4: "SMTP Error 101 - Invalid SSL or TLS usage in Jenkins."

How to Resolve SMTP Error 101 - Step-by-Step Solution:

To resolve SMTP Error 101, follow these steps:

1. Review your configurations: Double-check your SMTP settings and ensure they align with the configurations provided in the SMTP server's documentation.
2. Check SSL or TLS settings: Verify that SSL or TLS configurations are accurate and match the requirements of your SMTP server.
3. Google SMTP-specific solution: If using Google SMTP, enable "Less Secure Sign-In Technology" for your Google account and consider implementing the following configurations to address the error.

By carefully examining and correcting these configurations, you can effectively resolve SMTP Error 101 in both phpmailer and Jenkins environments.