This wont really be possible. Characters like that are not available on valid external email addresses. Unicode at most could be supported at the domain end by not the local user end.
Some mail servers are supporting this a little more, so you could send emails to an address with unicode on a server that supports it but as it stands Coldfusion wont allow it. Even Google don't allow creation of emails like this. Although they will allow transporting emails.
I use the isEmail() java class because it provides better validation than isValid("email") and provides consistent results on multiple platforms (Java, PHP & C#).
According to this RFC 321 compliant email validation library, the results are below:
frédéric.email@example.com = "Address is valid".
κείμενο@toto.com = "Address is valid but has an unusual initial letter"
I was going to recommend using Mandrill's API for sending since they have lots of advanced SMTP options, but apparently they aren't able to send email to addresses that have UTF-8 characters in the email prefix either.
Although MailChimp can process UTF-8 characters in most parts of our application, we cannot process UTF-8 characters in your subscribers' email address prefixes. We do accept Internationalized Domain Name (IDN) servers, so it’s alright to have UTF-8 characters in the domain name.
For example, we’ll block direcciónelectrónica@domain.com because the international characters are in the prefix, but we'll allow an address like test@ñoñó1234.com, where the characters are in the domain.
If anyone finds a mail server capable of sending to an address with UTF-8 characters in the prefix, please respond in this post. Thanks.