SMTP test mail doesn't work

Hello… I have a problem trying to get working the smtp basic configuration with a poste.io server I have in the same sever (both using docker).
I’ve been reading a lot and trying to apply many many suggestions and solution that worked for others, but not for me: I still have the red message telling there was a problem sending the mail.

My mail server works with no problem. I can send and recive mails and it seems all certs are ok.

If anyone can help me to solve the problem, it would be great because I’ve spend much time searching and trying and no luck.

Here is my config.php

{
“htaccess.RewriteBase”: “/”,
“memcache.local”: “\OC\Memcache\APCu”,
“apps_paths”: [
{
“path”: “/var/www/html/apps”,
“url”: “/apps”,
“writable”: false
},
{
“path”: “/var/www/html/custom_apps”,
“url”: “/custom_apps”,
“writable”: true
}
],
“upgrade.disable-web”: true,
“instanceid”: “REMOVED SENSITIVE VALUE”,
“passwordsalt”: “REMOVED SENSITIVE VALUE”,
“secret”: “REMOVED SENSITIVE VALUE”,
“trusted_domains”: [
server.mercenariosairsoftvlc.com
],
“datadirectory”: “REMOVED SENSITIVE VALUE”,
“dbtype”: “mysql”,
“version”: “28.0.4.1”,
“overwrite.cli.url”: “https://server.mercenariosairsoftvlc.com”,
“dbname”: “REMOVED SENSITIVE VALUE”,
“dbhost”: “REMOVED SENSITIVE VALUE”,
“dbport”: “”,
“dbtableprefix”: “oc_”,
“mysql.utf8mb4”: true,
“dbuser”: “REMOVED SENSITIVE VALUE”,
“dbpassword”: “REMOVED SENSITIVE VALUE”,
“installed”: true,
“trusted_proxies”: “REMOVED SENSITIVE VALUE”,
“overwriteprotocol”: “https”,
“maintenance_window_start”: 1,
“memcache.locking”: “\OC\Memcache\Redis”,
“memcache.distributed”: “\OC\Memcache\Redis”,
“redis”: {
“host”: “REMOVED SENSITIVE VALUE”,
“password”: “REMOVED SENSITIVE VALUE”,
“port”: 6379
},
“default_phone_region”: “ES”,
“mail_from_address”: “REMOVED SENSITIVE VALUE”,
“mail_smtpmode”: “smtp”,
“mail_sendmailmode”: “smtp”,
“mail_domain”: “REMOVED SENSITIVE VALUE”,
“mail_smtphost”: “REMOVED SENSITIVE VALUE”,
“mail_smtpport”: “587”,
“mail_smtpauthtype”: “”,
“mail_smtpstreamoptions”: {
“ssl”: {
“allow_self_signed”: “true”,
“verify_peer”: “false”,
“verify_peer_name”: “false”
}
},
“loglevel=0”: “”,
“allow_local_remote_servers”: “true”,
“mail_smtpdebug”: “true”,
“app.mail.verify-tls-peer”: “false”,
“maintenance”: false,
“mail_smtpauth”: 1,
“mail_smtpname”: “REMOVED SENSITIVE VALUE”,
“mail_smtppassword”: “REMOVED SENSITIVE VALUE”,
“debug”: “true”,
“mail_smtpsecure”: “ssl”
}

it would be nice if you would post logfiles… from both… your NC and your posteo-server.

maybe it’s getting clearer by the errormessages where/what the problem is.

posteo recommends this
Postausgangsserver (SMTP):
mit SSL-/TLS-Verschlüsselung über Port 465 oder
mit STARTTLS über Port 587

Posteingangsserver (IMAP):
mit SSL-/TLS-Verschlüsselung über Port 993 oder
mit STARTTLS über Port 143 (sorry. german)

apart from that… how have you installed your NC and serverenvironment.

as I read this: are you running with a selfsigned certificate?