I've started a partial check of mail addresses. The current beta
will check the domains of mail addresses (the part after the "@"). Xenu
makes a DNS request for MX records.
If Xenu can't find the file DNSAPI.DLL, it will check nothing. If Xenu
cannot find a host or an MX record for it, it will report the error "no
such host". If Xenu does find an MX record, it will output "skip type"
Thus, the new version will only find broken domains of mail addresses.
It doesn't check whether the user exists. The reason is that I doubt
that there is an exact check. (For obvious reason: it would help