==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release):0.9.9
- Deployed downloadable installer
- Linux/BSD distribution name and version: ubuntu 18.04.4
- Store mail accounts in which backend: MySQL
- Web server: Nginx
- Manage mail accounts with iRedAdmin-Pro: yes
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====
goed day everyone

i have a problem white my php based mail clients connecting to the server
if they try to connect to the server they get a error along the lines of: Unable to connect with TLS encryption (nextcloud)

full list of phpclients
Nextcloud 17.0.2
Librenms 1.59
unifi controller atag_5.11.46_12723

log
Jan 28 08:52:05 mail postfix/submission/smtpd[55326]: connect from unknown[10.10.50.6]
Jan 28 08:52:05 mail postfix/submission/smtpd[55326]: SSL_accept error from unknown[10.10.50.6]: -1
Jan 28 08:52:05 mail postfix/submission/smtpd[55326]: warning: TLS library problem: error:14094418:SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca:../ssl/record/rec_layer_s3.c:1528:SSL alert number 48:
Jan 28 08:52:05 mail postfix/submission/smtpd[55326]: lost connection after STARTTLS from unknown[10.10.50.6]
Jan 28 08:52:05 mail postfix/submission/smtpd[55326]: disconnect from unknown[10.10.50.6] ehlo=1 starttls=0/1 commands=1/2