SMTP-Relay no function with MD5

What type of hardware are you using: Virtual machine
What YunoHost version are you running: 12.0.11 (stable).
How are you able to access your server: SSH
Direct access via physical keyboard/screen

Describe your issue

Hello,

I have an urgent problem. I am using an SMTP relay. But the SMTP relay refuses to accept the e-mails. According to the provider, the problem is due to the MD5 checksum, which has obviously been obsolete for some time or represents a security risk in conjunction with /etc/postfix/sasl_passwd.

This is the log from the provider’s point of view:

Jan 31 13:16:42 francium postfix/smtpd[4308]: warning: xxxx.dip0.t-ipconnect.de[87.179.94.xxx]: SASL DIGEST-MD5 authentication failed: authentication failure, sasl_username=smtp-relay@xxxx.francium.selfhost.de
Jan 31 13:25:07 francium postfix/smtpd[4179]: warning: xxxx.dip0.t-ipconnect.de[87.179.94.xxx]: SASL DIGEST-MD5 authentication failed: authentication failure, sasl_username=smtp-relay@xxxx.francium.selfhost.de

The provider has given me the following additional information as a link, which deals with the issue. Unfortunately, I am at the end of my know-how to be able to assess this. Here is the link: Is it possible to disable CRAM-MD5 authentication for the postfix smtpd server? - Server Fault

However, Yunohost is set up correctly as it works with other SMTP relays. I have repeated a test several times. However, I would like to use the actual SMTP relay of my provider.

Is there a specialist here who can help me?

Share relevant logs or error messages

Jan 31 13:16:42 francium postfix/smtpd[4308]: warning: xxxx.dip0.t-ipconnect.de[87.179.94.xxx]: SASL DIGEST-MD5 authentication failed: authentication failure, sasl_username=smtp-relay@xxxx.francium.selfhost.de
Jan 31 13:25:07 francium postfix/smtpd[4179]: warning: xxxx.dip0.t-ipconnect.de[87.179.94.xxx]: SASL DIGEST-MD5 authentication failed: authentication failure, sasl_username=smtp-relay@xxxx.francium.selfhost.de