status=deferred when sending a mail with Postfix on my VPS

I come here after having searched on the net and groped for long.

I got a VPS on Debian 11 with the domain name leibnizproject.com and I want to send mails from it, with the command mail -s "test" myPersonalEmailAddress

But no mail is received and I get the following result (in /var/log/mail.info):

Jan 26 14:46:14 mail postfix/qmgr[1762]: 8ABCB1401CD: from=<[email protected]>, size=354, nrcpt=2 (queue active)
Jan 26 14:46:20 mail postfix/smtp[3288]: connect to mx-eu.mail.am0.yahoodns.net[188.125.72.73]:25: Connection timed out
Jan 26 14:46:20 mail postfix/smtp[3288]: C3ABC140201: to=<myPersonalEmailAddress>, relay=none, delay=60, delays=0.02/0.01/60/0, dsn=4.4.1, status=deferred (connect to mx-eu.mail.am0.yahoodns.net[188.125.72.7>
Jan 26 14:46:44 mail postfix/smtp[3291]: connect to mx-eu.mail.am0.yahoodns.net[188.125.72.73]:25: Connection timed out
Jan 26 14:46:51 mail postfix/pickup[3150]: 0CFAE140204: uid=0 from=<[email protected]>
Jan 26 14:46:51 mail postfix/cleanup[3286]: 0CFAE140204: message-id=<[email protected]>
Jan 26 14:46:51 mail postfix/qmgr[1762]: 0CFAE140204: from=<[email protected]>, size=343, nrcpt=1 (queue active)

Here is the content of /etc/postfix/postfix/main.cf (comments removed)

smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
biff = no
append_dot_mydomain = no
readme_directory = no
compatibility_level = 2
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_tls_security_level=may
smtp_tls_CApath=/etc/ssl/certs
smtp_tls_security_level=may
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
myhostname = leibnizproject.com
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = leibnizproject.com
mydestination = leibnizproject.com, 197t.l.hostens.cloud, localhost.l.hostens.cloud, localhost
relayhost =
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
inet_protocols = all

I've written leibnizproject.com as a hostname in the panel of my internet service provider.

This port scanner tells me that my port 25 is 'filtered'.

Is a reboot useful after having modified main.cf?

The "status=deferred" message in a Postfix log indicates that the email message has been temporarily deferred and will be retried later and its queued. This may occur for several reasons, but in your case, most probably the case is:

Spam filtering on destination mail server: The recipient mail server is blocking the email as potential spam, since there is no PTR & SPF records defined or your server IP address is listed in DNSBL.