@blackdoginet Please set your site in debugging mode than we should be able to see more detailed information. You may not be on GoDaddy?
https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting#godaddy

I am not on GoDaddy its my own VPS
Debugging switched on.
FYI PHPmailer V 5.6.2 SMTP also fails on this machine but runs on PHP 5.6

Further last few lines from output from
openssl s_client -starttls smtp -crlf -connect smtp.mydomain.net:587

Start Time: 1486712119
Timeout : 300 (sec)
Verify return code: 0 (ok)

250 DSN
quit
221 2.0.0 Bye
closed
show there is no problem with certificates or firewalls

hmm the last guess i have is:

Openssl Check performed openssl s_client -starttls smtp -crlf -connect smtp.mydomain.net:587

Here you use 587 as port number.

In Your Configuration you uploaded it is 25

smtpport: 25

If this is not the problem i suggest to move this issue with sending mails to a server forum or the joomla forum (forum.joomla.org) as you are the only one who reports such issues and i got some feedback that it is working fine on other sites with SMTP & PHP7.

It is an issue I switched to port 25 to use SSL. My mail server uses STARTTLS so I originally used 587 that. NEITHER work

It is reported multiple times on extension forums see http://www.fox.ra.it/forum/5-support/11835-php-7-error.html?start=10 and also last 2 comments in phpmailer issue PHPMailer/PHPMailer#953
It is not my configuration

Deepest Apologies. Was my config. Fail2Ban running on mail server blocking smtp login
Issue closed.
Sorry

Glad you solved it. Thanks for the update ?

I have a exemple with my full noob configuration with Debian 9.5 and PHP7.2 and, before, PHP7.0 and, the same bog, SMTP doesn't work correctly.

1. My light serveur for test : https://github.com/ZerooCool/Linux-Search-Engine-Optimisation/blob/master/installation/3-installer-le-serveur-dans-le-conteneur.sh
2. My light installation with Joomla (last version) https://github.com/ZerooCool/Linux-Search-Engine-Optimisation/blob/master/installation/4-installer-joomla.sh

Option SMTP on Joomla, with port 587 and SSL/TLS or STARTTLS, with identification.

I have this message in french, and, mail doesn't work
Annonce
Impossible de connecter par SMTP https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting
Erreur
Le test d'e-mail n'a pu être envoyé.

cd /var/log/user.log
Jul 31 17:17:42 : [31-Jul-2018 17:17:42 Europe/Berlin] mail() on [/var/www/html/libraries/vendor/phpmailer/phpmailer/class.phpmailer.php:702]: To: mail@domain.com -- Headers: Date: Tue, 31 Jul 2018 17:17:42 +0200 From: =?utf-8?Q?Green_NRJ_-Alternatives_pour_une_soci=C3=A9t=C3=A9_collaborati?= =?utf-8?Q?ve_et=C3=A9cologique=2E?= mail@domain.com Message-ID: <... ...@... ...> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit

Now, more info,

1. I don't have SSL with my website. You have my config on the top.

2. 2/3 mails SMTP never work (smtp.visionduweb.com and ns0.ovh.com not work)
   1/3 work. SMTP with SSL/TLS and Gmail on the 465 port work good.

3. I don't use Fail2ban.

4. I don't have enable “Less Secure Apps” on my Gmail account and mail work good.

Mail don't work with 2 other smtp serveur (smtp.visionduweb.com and ns0.ovh.com not work)
I can use this SMTP with redmine, or, mediawiki, and, work good.

For this test, i have use my VPS OVH with Debian 9.5, and, Virtualbox with Debian 9.5.
Exactly the same result, with the same config.

@ZerooCool Thanks for your Comment, but please open a new Issue as Comments on closed Issues didn't get much Notice.