Neither com.com nor mach.com.com have a valid MX record, and the A record IP for these domains does not accept an SMTP connection, so at the moment they are not valid email addresses. Unless, of course, a local mail server rewrites these addresses into something different, or someone turns on the mail server at those addresses in five minutes, in which case they most certainly are :-)
Just because an MX record isn't propagated to you doesn't mean it doesn't exists. Many companies and organisations have a DNS that looks differently internally than externally. Heck, even my local network consisting of a whopping 3 machines has an internal DNS different from the outside world.

It's not possible to determine a given address exists. What you can do is check whether a given address is syntactically valid (surprisingly many strings are valid addresses - a valid address doesn't have to contain a '@' - this posting will contain many, many valid addresses). But it doesn't mean that an address that is syntactically (according to RFC 822 or any of its successors) invalid isn't deliverable.

Another alternative is to send a message to see what happens. If you get a reply that looks like it was written by a human, it's probably a valid address. (Of course, it may have become invalid after the reply was send....). If you get a bounce, it may be invalid (but I can bounce messages from mutt).

ucbvax!ibm4java!dec4javafan!javafan

In reply to Re^3: About validating mail id by JavaFan
in thread About validating mail id by pavanmach

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