In addition to (internal) recipients a message might also be addressed to external email recipients. Those external recipients will get a translated copy of the original message delivered via SMTP. Acknowledgment is not possible for external email recipients and of course traceability is also not provided.
You can use external recipients if you want to send messages to people that are not system users. Note that due to message translation not all information present in the original message might be available with in the externally sent message.
Addresses for external email recipients must conform to the regular expression shown in listing 1. For example: firstname.lastname@redbex.net would be a valid address, while "Lastname, firstname" <firstname.lastname@redbex.net> would not be valid.
[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])? |
Listing 1: Regular expression used for validating the email addresses of external email recipients
