==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release):  0.9.9 MARIADB edition.
- Deployed with iRedMail Easy or the downloadable installer? Downloadable Installer
- Linux/BSD distribution name and version:  Ubuntu 18.04.3 LTS bionic
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx): NGINX
- Manage mail accounts with iRedAdmin-Pro? NO
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

Its a fresh installation. Not my first either.

I am testing email in roundcube.

I can receive fine.

When I try to send I get the following error in Roundcube:

SMTP Error (454): Authentication failed.

I then receive an email in my inbox with this content:

Transcript of session follows.

Out: 220 webserver.bio-olives.com ESMTP Postfix
In:  EHLO bio-olives.com
Out: 250-webserver.bio-olives.com
Out: 250-PIPELINING
Out: 250-SIZE 15728640
Out: 250-ETRN
Out: 250-STARTTLS
Out: 250-ENHANCEDSTATUSCODES
Out: 250-8BITMIME
Out: 250-DSN
Out: 250 SMTPUTF8
In:  STARTTLS
Out: 454 4.7.0 TLS not available due to local problem
In:  RSET
Out: 530 5.7.0 Must issue a STARTTLS command first
In:  QUIT
Out: 221 2.0.0 Bye

For other details, see the local mail logfile

Finally my relevant maillog is:

Sep  6 00:28:58 webserver postfix/submission/smtpd[29362]: warning: cannot get RSA private key from file "/etc/letsencrypt/live/bio-olives.com.com/privkey.pem": disabling TLS support
Sep  6 00:28:58 webserver postfix/submission/smtpd[29362]: warning: TLS library problem: error:02001002:system library:fopen:No such file or directory:../crypto/bio/bss_file.c:290:fopen('/etc/l     etsencrypt/live/bio-olives.com.com/privkey.pem','r'):
Sep  6 00:28:58 webserver postfix/submission/smtpd[29362]: warning: TLS library problem: error:20074002:BIO routines:file_ctrl:system lib:../crypto/bio/bss_file.c:292:
Sep  6 00:28:58 webserver postfix/submission/smtpd[29362]: warning: TLS library problem: error:140B0002:SSL routines:SSL_CTX_use_PrivateKey_file:system lib:../ssl/ssl_rsa.c:540:
Sep  6 00:28:58 webserver postfix/submission/smtpd[29362]: connect from localhost[127.0.0.1]
Sep  6 00:28:58 webserver roundcube: ERROR: Invalid response code received from server (454)
Sep  6 00:28:58 webserver roundcube: ERROR: Invalid response code received from server (530)
Sep  6 00:28:58 webserver postfix/cleanup[29364]: 46Pb2L127Kz20Tk: message-id=<46Pb2L127Kz20Tk@webserver.bio-olives.com>
Sep  6 00:28:58 webserver postfix/qmgr[29183]: 46Pb2L127Kz20Tk: from=<double-bounce@webserver.bio-olives.com>, size=938, nrcpt=1 (queue active)
Sep  6 00:28:58 webserver postfix/submission/smtpd[29362]: disconnect from localhost[127.0.0.1] ehlo=1 starttls=0/1 rset=0/1 quit=1 commands=2/4
Sep  6 00:28:58 webserver roundcube: <t6ctp3k2> SMTP Error: Authentication failure: Invalid response code received from server (Code: 454) in /opt/www/roundcubemail-1.3.8/program/lib/Roundcube/     rcube.php on line 1667 (POST /mail/?_task=mail&_unlock=loading1567722537184&_lang=en_US&_framed=1&_action=send)
Sep  6 00:28:58 webserver postfix/cleanup[29364]: 46Pb2L1W6Hz20Tm: message-id=<46Pb2L127Kz20Tk@webserver.bio-olives.com>
Sep  6 00:28:58 webserver postfix/qmgr[29183]: 46Pb2L1W6Hz20Tm: from=<double-bounce@webserver.bio-olives.com>, size=1099, nrcpt=1 (queue active)
Sep  6 00:28:58 webserver postfix/local[29368]: 46Pb2L127Kz20Tk: to=<postmaster@webserver.bio-olives.com>, orig_to=<postmaster>, relay=local, delay=0.08, delays=0.03/0.03/0/0.02, dsn=2.0.0, sta     tus=sent (forwarded as 46Pb2L1W6Hz20Tm)
Sep  6 00:28:58 webserver postfix/qmgr[29183]: 46Pb2L127Kz20Tk: removed
Sep  6 00:28:58 webserver postfix/pipe[29370]: 46Pb2L1W6Hz20Tm: to=<postmaster@bio-olives.com>, orig_to=<postmaster>, relay=dovecot, delay=0.05, delays=0/0.02/0/0.03, dsn=2.0.0, status=sent (de     livered via dovecot service (doveconf: Warning: SSLv2 not supported by OpenSSL. Please consider removing it from ssl_protocols.))
Sep  6 00:28:58 webserver postfix/qmgr[29183]: 46Pb2L1W6Hz20Tm: removed