Ubuntu 18.04 - SMTP ERROR: Failed to connect to server: Connection refused (111)

I have this new error since 2 weeks on my server.

I haven't touched the code or anything.

I usually send mail trough PHPMailer, but I noticed Thunderbird won't work anymore also.

I'm on Ubuntu 18.04 LTS. I did apt get update/upgrade (+ Reboot) but it didn't change anything

Sending a mail trough the "mail" command works fine :

echo "test" | mail -s "sujet" [email protected]

Here is my postfix main.cf :

# See /usr/share/postfix/main.cf.dist for a commented, more complete version


# Debian specific:  Specifying a file name will cause the first
# line of that file to be used as the name.  The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname

smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

readme_directory = no

# See http://www.postfix.org/COMPATIBILITY_README.html -- default to 2 on
# fresh installs.
compatibility_level = 2



# TLS parameters
# smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
# smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_tls_cert_file=/etc/letsencrypt/live/mail.my-domain.com/fullchain.pem
smtpd_tls_key_file=/etc/letsencrypt/live/mail.my-domain.com/fullchain.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.

smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated defer_unauth_destination
# myhostname = vps811910.openstacklocal
myhostname = mail.my-domain.com
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
# mydestination = $myhostname, vps811910, localhost.localdomain, localhost, mail.my-domain.com
mydestination = $myhostname, vps811910, localhost.localdomain, localhost, my-second-domain.com
relayhost = 
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = loopback-only
inet_protocols = all

PHP Mailer :

https://codeshare.io/eVxYP7

please try to see this post on StackOverflow maybe it solve also for you.

However, looking at your PHP Mailer, i see a strange value here:

$mail->Host = 'my-second-domain.com';

This should contain your smtp mail host, for example:

$mail->Host = "smtp.gmail.com";