IONOS blocks non-delivery reports and out-of-office messages

The provider IONOS has decided to block all emails with an empty sender field since January 2024. Unfortunately, Exchange sends non-delivery reports (NDRs) and out-of-office notifications (OOF) without a sender address. This is actually correct according to the SMTP FAQ's, but IONOS still blocks them with the error message "Sender address is not allowed"

MultiSendcon (both the Lite version and the full version) can be used to solve this problem. Both versions automatically fill in the sender address from the message content or if there is none, use a fixed address you can configure in the MultiSendcon Admin interface.