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.