I cannot respond to an incident because the email address is marked as invalid in the contact record.
Contacts, Email Address, Sending a Response Message
Oracle Service Cloud, All versions
When the techmail utility processes email messages, it detects hard bounces from sending mail servers. If a hard bounce is detected, the contact's email address is flagged as invalid. When viewing the contact record from the console, a red icon displays next to the email field.
If you determine that an email address that is flagged as invalid is actually valid, you can edit the email address slightly and save the record. Then, re-open the record and save it back with the valid email address.
For example, you can add .invalid to the end of the email address and save the contact record. Then, re-open the contact record, remove the .invalid extension and the record saves without the invalid flag. Then, you can send a response to your incident.