Problems with E-Mail after installation of discourse

Hey guys,
I have currently difficulties with the emails of a newly installed discourse.

Here is my setup:

I installed discourse with docker.
The smtp server is an Exchange 2019 Server
My E-Mail configuration is as follows:

>DISCOURSE_SMTP_ADDRESS: 10.XX.X.106
>DISCOURSE_SMTP_PORT: 587
>DISCOURSE_SMTP_USER_NAME: forumverwaltung@xxxx.internal
>DISCOURSE_SMTP_PASSWORD: *the password of the smtp user*
>DISCOURSE_SMTP_AUTHENTICATION: login
>DISCOURSE_SMTP_ENABLE_START_TLS: true
>DISCOURSE_SMTP_OPENSSL_VERIFY_MODE: none

I already tried everything that is present on the page: Troubleshooting email on a new Discourse install

And also I already run discourse-doctor, which can successfully sends emails.
The problem is that discours only authenticate with the smtp server and does not send any e-mails.
I discovered that over the smtp logs of the exchange server:

>2020-12-17T21:22:54.377Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,1,10.XX.X.106:587,10.XX.X.123:49540,>,"220 xxxxx.xxxxx.dev Microsoft ESMTP MAIL Service ready at Thu, 17 Dec 2020 22:22:53 +0100",
>2020-12-17T21:22:54.377Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,2,10.XX.X.106:587,10.XX.X.123:49540,<,EHLO localhost.localdomain,
>2020-12-17T21:22:54.377Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,3,10.XX.X.106:587,10.XX.X.123:49540,>,250  xxxxx.xxxxx.dev Hello [10.XX.X.123] SIZE 104857600 PIPELINING DSN ENHANCEDSTATUSCODES STARTTLS AUTH GSSAPI NTLM LOGIN 8BITMIME BINARYMIME CHUNKING SMTPUTF8,
>2020-12-17T21:22:54.378Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,4,10.XX.X.106:587,10.XX.X.123:49540,<,STARTTLS,
>2020-12-17T21:22:54.378Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,5,10.XX.X.106:587,10.XX.X.123:49540,>,220 2.0.0 SMTP server ready,
>2020-12-17T21:22:54.378Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,6,10.XX.X.106:587,10.XX.X.123:49540,*," CN=xxxxx.xxxxx.dev CN=R3, O=Let's Encrypt, C=US 03870D309B69ED14DAEFE37D96B36FFB01A7 A2539D22A15F71B0109A4F49847254B1DB58D18B 2020-12-14T19:53:13.000Z 2021-03-14T19:53:13.000Z xxxxx.xxxxx.dev",Sending certificate Subject Issuer name Serial number Thumbprint Not before Not after Subject alternate names
>2020-12-17T21:22:54.390Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,7,10.XX.X.106:587,10.XX.X.123:49540,*,,"TLS protocol SP_PROT_TLS1_2_SERVER negotiation succeeded using bulk encryption algorithm CALG_AES_256 with strength 256 bits, MAC hash algorithm CALG_SHA_384 with strength 0 bits and key exchange algorithm CALG_ECDH_EPHEM with strength 384 bits"
>2020-12-17T21:22:54.390Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,8,10.XX.X.106:587,10.XX.X.123:49540,<,EHLO localhost.localdomain,
>2020-12-17T21:22:54.390Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,9,10.XX.X.106:587,10.XX.X.123:49540,*,,Client certificate chain validation status: 'EmptyCertificate'
>2020-12-17T21:22:54.390Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,10,10.XX.X.106:587,10.XX.X.123:49540,*,,TlsDomainCapabilities='None'; Status='NoRemoteCertificate'
>2020-12-17T21:22:54.390Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,11,10.XX.X.106:587,10.XX.X.123:49540,>,250  xxxxx.xxxxx.dev Hello [10.XX.X.123] SIZE 104857600 PIPELINING DSN ENHANCEDSTATUSCODES AUTH GSSAPI NTLM LOGIN 8BITMIME BINARYMIME CHUNKING SMTPUTF8,
>2020-12-17T21:22:54.391Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,12,10.XX.X.106:587,10.XX.X.123:49540,<,AUTH LOGIN,
>2020-12-17T21:22:54.392Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,13,10.XX.X.106:587,10.XX.X.123:49540,>,334 <authentication response>,
>2020-12-17T21:22:54.392Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,14,10.XX.X.106:587,10.XX.X.123:49540,>,334 <authentication response>,
>2020-12-17T21:22:54.419Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,15,10.XX.X.106:587,10.XX.X.123:49540,*,SMTPSubmit SMTPAcceptAnyRecipient BypassAntiSpam AcceptRoutingHeaders,Set Session Permissions
>2020-12-17T21:22:54.419Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,16,10.XX.X.106:587,10.XX.X.123:49540,*,forumverwaltung@xxxx.internal user,authenticated
>2020-12-17T21:22:54.419Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,17,10.XX.X.106:587,10.XX.X.123:49540,*,,ASyncBackendLocator.BeginGetDatabaseToServerMappingInfo for user forum@xxx.dev.
>2020-12-17T21:22:54.425Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,18,10.XX.X.106:587,10.XX.X.123:49540,*,,AsyncBackendLocator.EndGetDatabaseToServerMappingInfo for user forum@xxx.dev
>2020-12-17T21:22:54.425Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,19,10.XX.X.106:587,10.XX.X.123:49540,*,,Setting up client proxy session to destination(s): exchange2019.xxxx.internal
>2020-12-17T21:22:54.440Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,20,10.XX.X.106:587,10.XX.X.123:49540,*,,Proxy session was successfully set up. Session for forumverwaltung@xxxx.internal will now be proxied
>2020-12-17T21:22:54.440Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,21,10.XX.X.106:587,10.XX.X.123:49540,>,235 2.7.0 Authentication successful,
>2020-12-17T21:22:54.575Z,EXCHANGE2019\Client Frontend EXCHANGE2019,08D8A2D1398FB749,22,10.XX.X.106:587,10.XX.X.123:49540,-,,Local

Can someone help me with this topic?

Thanks ahead

-PZ