Mail server programs originally verified user mailboxes and always bounced bad email addresses.

Because of spam, it is rare for a SMTP server to verify users via the VRFY command. Verifying valid user mailbox names server makes a domain vulnerable to dictionary attacks, i.e., a hacker uses a list of millions of popular mailbox names and asks the mail server to verify which ones are valid for its domain. The list of valid email addresses can then be sold to spammers.

If emails are bounced, a spammer can eliminate them from his list of valid email addresses, like you are. Mail administrators may turn off email bouncing to foil attempts to determine which email accounts are active. Unfortunately, this makes it harder for valid emailers to maintain their email lists.

Checking the syntax of email addresses might catch some email addresses that are incorrectly. You might be able to catch a few additional defunct email addresses by parsing the domain name out of the email address and querying a domain name server to see if the domain still exists.

The best that you can probably do is check for bad syntax, defunct domains, and then save any bounced emails and programmatically parse out the original recipient address and then remove it from your database. You might want to check if bounced emails included a forwarding address.

If a new mail protocol is ever adopted that is more secure than SMTP, more mail servers may support verification once spam is less of a problem.

>The database contains many email adresses. Some of those adresses are old others are recent.
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>Is there a way to test for the validity of an address before sending a message to that address?