E-Mail's without the company address are not being sent out

When sending an E-Mail with the company address, the E-Mail is sent without any issues.

When sending an E-Mail with another address, the E-Mail is not always sent out:

1.The error only occurs in connection with the E-Mail's that are triggered when reminders, warnings, alarms and errors occur.

2.Via Extra>Setup>System>Send test email: the E-Mail works.

3.When requesting a new password in the login area: the E-Mail works.

4.Via Extra>Setup>Email reports: the E-Mail works.

This is a SMTP configuration that needs to be adapted on the customer's IT side.