Hi @shoaibkk , thanks for your help.
I’m still stuck with this issue and I think very soon all my mail-server’s domains will have the same problem. 
I cannot give you access to the server, but I can share the domain name privately and we can have a TeamViewer session, so you can access the server.
SSL emails are not working for this domain, I shared the error in Thunderbird, and here is the error in Laravel:
Unable to connect with STARTTLS: stream_socket_enable_crypto(): SSL operation failed with code 1. OpenSSL Error messages: error:0A000086:SSL routines::certificate verify failed
When I re-issued SSL Mailserver in CyPanel, the following got updated, but still I’ve cert Error (see scr-shot) and emails are not working.
smtpd_tls_cert_file = /etc/pki/dovecot/certs/dovecot.pem
smtpd_tls_key_file = /etc/pki/dovecot/private/dovecot.pem
laravel.log
[2024-05-04 12:03:18] local.ERROR: Unable to connect with STARTTLS: stream_socket_enable_crypto(): SSL operation failed with code 1. OpenSSL Error messages:
error:0A000086:SSL routines::certificate verify failed {"userId":5,"exception":"[object] (Symfony\Component\Mailer\Exception\TransportException(code: 0): Unable to connect with STARTTLS: stream_socket_enable_crypto(): SSL operation failed with code 1. OpenSSL Error messages:
error:0A000086:SSL routines::certificate verify failed at /home/example.com/laravel/vendor/symfony/mailer/Transport/Smtp/Stream/SocketStream.php:171)
[stacktrace]
laravel .env
MAIL_MAILER=smtp
MAIL_HOST=mail.example.com
MAIL_PORT=587
[email protected]
MAIL_ENCRYPTION=tls
MAIL_FROM_ADDRESS="[email protected]"
postfix.log
May 5 19:51:09 server1 postfix/anvil[901637]: statistics: max connection rate 1/60s for (smtp:45.88.90.38) at May 5 19:47:48
May 5 19:51:09 server1 postfix/anvil[901637]: statistics: max connection count 1 for (smtp:45.88.90.38) at May 5 19:47:48
May 5 19:51:09 server1 postfix/anvil[901637]: statistics: max cache size 1 at May 5 19:47:48
May 5 19:52:53 server1 postfix/smtpd[901810]: connect from unknown[xxx.118.xxx.118]
May 5 19:52:54 server1 postfix/smtpd[901810]: warning: unknown[xxx.118.xxx.118]: SASL LOGIN authentication failed: Invalid authentication mechanism
May 5 19:52:54 server1 postfix/smtpd[901810]: lost connection after AUTH from unknown[xxx.118.39.xxx]
May 5 19:52:54 server1 postfix/smtpd[901810]: disconnect from unknown[xxx.118.39.xxx] ehlo=1 auth=0/1 commands=1/2
May 5 20:08:14 server1 postfix/anvil[902275]: statistics: max cache size 1 at May 5 20:04:54
May 5 20:11:02 server1 postfix/qmgr[807922]: 65404107D65: from=<>, size=3105, nrcpt=1 (queue active)
May 5 20:13:14 server1 postfix/smtp[902555]: 65404107D65: host natwest.co.uk[13.107.213.69] refused to talk to me: 421 Downstream server error
May 5 20:15:07 server1 dovecot: imap-login: Disconnected: Connection closed: SSL_accept() failed: error:0A000102:SSL routines::unsupported protocol (no auth attempts in 1 secs): user=<>, rip=xxx.210.31.172, lip=xxx.254.xxx.239, TLS handshaking: SSL_accept() failed: error:0A000102:SSL routines::unsupported protocol, session=<7UTom7oXjMrN0h+s>
May 5 20:15:20 server1 postfix/smtpd[902677]: connect from unknown[xxx.32.xxx.80]
May 5 20:15:20 server1 postfix/smtpd[902677]: warning: unknown[xxx.32.xxx.80]: SASL LOGIN authentication failed: Invalid authentication mechanism
May 5 20:15:21 server1 postfix/smtpd[902677]: lost connection after AUTH from unknown[xxx.32.xxx.80]
Can you please contact me by email and let me know when you’re available?
Many thanks