Not allowed to send emails from WP

Hello,

I'm facing a problem.
I have a debian 10 with a LAMP server installed. I have hosted a lot of Wordpress Websites on this server.

I have the same issue to all.

I'm trying to set up WP Smtp mail by WP Forms, as I fill the form with the SMTP credentials (I have triple checked them and they are correct, checked by connecting via outlook and apple mail) when I try to send an email I get the error below.

I can't find any issues or a solution about this problem. I believe that the lamp server is blocking the outgoing smtp connections.

Note that I'm using a shared server with cpanel on another provider for my mail server and I'm using linode for hosting my websites. The domains are set to the other provider and I only set the A record for the website url.

Thanks in advance.

Error
Versions:
WordPress: 5.8.2
WordPress MS: No
PHP: 7.4.14
WP Mail SMTP: 3.1.0
Params:
Mailer: smtp
Constants: No
ErrorInfo: SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting
Host: mail.tustore.gr
Port: 587
SMTPSecure: string(0) ""
SMTPAutoTLS: bool(true)
SMTPAuth: bool(true)
Server:
OpenSSL: OpenSSL 1.1.1i 8 Dec 2020
Apache.mod_security: No
Debug:
Email Source: WP Mail SMTP
Mailer: Other SMTP
SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting
SMTP Debug:
2021-11-11 14:54:11 Connection: opening to mail.tustore.gr:587, timeout=300, options=array()
2021-11-11 14:54:42 Connection failed. Error #2: stream_socket_client(): unable to connect to mail.tustore.gr:587 (Connection timed out) [/home/tustore/tustore/public_html/wp-includes/PHPMailer/SMTP.php line 388]
2021-11-11 14:54:42 SMTP ERROR: Failed to connect to server: Connection timed out (110)
SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting