Hi @Klicklaar
Azure Communication Services resource is on the default throttling tier, adding additional MailFrom addresses is not permitted. To enable this feature, please consider upgrading your sending limits.
A recent update to the Email Communication Services now restricts the creation of new MailFrom addresses and the enabling of engagement tracking if you are on the default throttling limit.
https://learn.microsoft.com/en-us/azure/communication-services/concepts/service-limits#email
kindly refer this thread: https://learn.microsoft.com/en-us/answers/questions/1630281/add-button-disabled-in-email-communication-service
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