Can't send SMTP emails

Hi there,

I’ve been struggling with this for a couple of hours: I can’t seem to be able to send email through smtp, error is always: Expected response code 250 but got code "550", with message "550 Invalid From address.

I know that sounds like an easy one, but whatever I put in variable “MAIL_FROM” I have the same error (I checked with my email provider to make sure). I’m using the same SMTP settings (on the same server) with my Nextcloud instance and everything works fine.

In the debug.log, is there a way to get more debug info to confirm which From Address is actually used? It behaves as if the ‘MAIL_FROM’ was ignored.

Here is the excerpt from my config.php :

define('MAIL_CONFIGURATION', true);
define('MAIL_TRANSPORT', 'smtp');
define('MAIL_SMTP_HOSTNAME', '');
define('MAIL_SMTP_PORT', 465);
define('MAIL_SMTP_ENCRYPTION', "ssl"); // Valid values are null (not a string "null"), "ssl" or "tls"

Here is my configuration:

Application version: 1.2.15
PHP version: 7.3.21
PHP SAPI: fpm-fcgi
HTTP Client: cURL
OS version: FreeBSD 12.1-RELEASE-p9
Database driver: mysql
Database version: 10.3.24-MariaDB 

Thanks in advance.

Cheers /jerome