OpenSSL on my server isn't able to verify the host certificate

Good morning, I can't connect via smtp using WP Mail SMTP and when I connect via ftp Filezilla says it doesn't support TLS.

I used Let's Encrypt from Centos Web Panel to get the SSL certificate.

Can you guys help me to solve this? I don't know how to do it. Thank you very much!

For example I get this error from WP Mail SMTP:

Code: [Select]

Versions:
WordPress: 5.4.6
WordPress MS: No
PHP: 5.6.37
WP Mail SMTP: 3.0.2

Params:
Mailer: smtp
Constants: No
ErrorInfo: SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting
Host: server720546
Port: 465
SMTPSecure: ssl
SMTPAutoTLS: bool(true)
SMTPAuth: bool(true)

Server:
OpenSSL: OpenSSL 1.0.1e-fips 11 Feb 2013

Debug:
Email Source: WP Mail SMTP
Mailer: Other SMTP
SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting

SMTP Debug:
2021-08-06 16:55:32 Connection: opening to ssl://server720546:465, timeout=300, options=array ()

2021-08-06 16:55:32 Connection failed. Error #2: stream_socket_client(): SSL operation failed with code 1. OpenSSL Error messages:error:14090086:SSL routines:ssl3_get_server_certificate:certificate verify failed [/home/domain/public_html/wp-includes/class-smtp.php line 299]

2021-08-06 16:55:32 Connection failed. Error #2: stream_socket_client(): Failed to enable crypto [/home/domain/public_html/wp-includes/class-smtp.php line 299]

2021-08-06 16:55:32 Connection failed. Error #2: stream_socket_client(): unable to connect to ssl://server720546:465 (Unknown error) [/home/domain/public_html/wp-includes/class-smtp.php line 299]

2021-08-06 16:55:32 SMTP ERROR: Failed to connect to server: (0)

SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting

Hi use server hostname and ensure ssl is installed for hostname.