unable to open connection to SMTP server

[lucyferu]

Describe the bug

trying to sync my sogo mail with my android email app and another self-hosted email app (cypht)

Context

• Hardware: VPS bought online
• YunoHost version: 11.0.11 (stable)
• I have access to my server: Through SSH | through the webadmin
• Are you in a special context or did you perform some particular tweaking on your YunoHost instance?: no
• Using, or trying to install package version/branch: 5.0.1~ynh1

Steps to reproduce

• If the error occurs in your browser, explain what you did:
  1. Open my android email app (is a fork of k9)
  2. added a new account
  3. tried to setup outgoing server/smtp after the ssl/tls/incoming one
  4. After loading for a while, it shows the error: Cannot connect to server (unable to open connection to SMTP server).

when i try to do the same thing on Cypht, i receive the error Could not add server: connection refused.

Expected behavior

simply connecting to the server

Logs

i read and tried this solution, but it didn't work for me. stunnel4 was already active, but there seems to some errors legged anyway:

● stunnel4.service - LSB: Start or stop stunnel 4.x (TLS tunnel for network dae>
     Loaded: loaded (/etc/init.d/stunnel4; generated)
     Active: active (running) since Sat 2023-01-28 21:25:32 CET; 2 days ago
       Docs: man:systemd-sysv-generator(8)
      Tasks: 2 (limit: 9507)
     Memory: 1.6M
        CPU: 759ms
     CGroup: /system.slice/stunnel4.service
             └─85035 /usr/bin/stunnel4 /etc/stunnel/sogo.conf

Jan 30 01:07:18 charming.monster stunnel[85035]: LOG5[0]: Connection closed: 56>
Jan 30 02:02:17 charming.monster stunnel[85035]: LOG5[1]: Service [Smtp-Starttl>
Jan 30 02:02:17 charming.monster stunnel[85035]: LOG5[1]: s_connect: connected >
Jan 30 02:02:17 charming.monster stunnel[85035]: LOG5[1]: Service [Smtp-Starttl>
Jan 30 02:02:18 charming.monster stunnel[85035]: LOG5[1]: Connection closed: 10>
Jan 30 10:13:19 charming.monster stunnel[85035]: LOG5[2]: Service [Smtp-Starttl>
Jan 30 10:13:19 charming.monster stunnel[85035]: LOG5[2]: s_connect: connected >
Jan 30 10:13:19 charming.monster stunnel[85035]: LOG5[2]: Service [Smtp-Starttl>
Jan 30 10:13:21 charming.monster stunnel[85035]: LOG5[2]: Connection closed: 31>
Jan 30 21:25:32 charming.monster stunnel[85035]: LOG5[main]: Log file reopened

also, this are the ynh logs.