What's Causing This Error
The SMTP 101 error can occur when there is a configuration issue with your SMTP settings. It can be:
- A Misconfigured port.
- An invalid SMTP host server.
- An invalid SMTP IP address.
- Invalid use of SSL or TLS.
However, this error commonly occurs with Google SMTP due to invalid SSL or TLS configurations.
Solution - Here's How To Resolve It
To resolve the error, re-look at your configurations, cross-check them with the configurations provided by the SMTP server's documentation, and ensure that you've configured them correctly.
Using Google SMTP, you could try the configurations shown below to resolve your error. First, however, you must enable "Less Secure Sign-In Technology" for your Google account.
Gmail SMTP server address: smtp.gmail.com
Gmail SMTP username: <YOUR-GMAIL-ACCOUNT> (enable less secure apps access)
Gmail SMTP password: <YOUR-GMAIL-PASSWORD>
Gmail SMTP port (TLS): 587 // for TLS Security
Gmail SMTP port (SSL): 465 // for SSL security
Requires SSL: Yes // use only with PORT 587 (if error)
Requires TLS: Yes // use only with PORT 465 (if error)
Requires authentication: Yes // enable authentication.
Requires secure connection: Yes // specify to enable SSL/TLS when sending the email.