The following code returns true:
select is_email('john.doe@acme.c')
The right email address should have had TLD ch for Switzerland instead of c.
Is it possible to extend the validation (optionally) to also check for the TLD validity such as contained in data.iana.org/TLD/tlds-alpha-by-domain.txt?
Or to add a SQL function to perform a DNS lookup for existance of an MX record?