In addition to determining if email addresses are valid/invalid, we can tell you many other things about the address:
Location of email and web servers – We can determine the country code, owner, region and city of the email server and the primary domain server (web site). This information will help our customers determine how they interact with their prospects/customers. For example, if you own a local landscaping company, sending product materials to someone in China may not be very useful.
Disposable email accounts – We can identify temporary or disposable email accounts. We track hundreds of these services (trash-mail, 10minutemail, etc.) and we will flag disposable accounts. This information will help our customers weed-out useless email addresses. For example, if your website requires an email address to download a whitepaper, we can detect bogus disposable email accounts and prevent you from wasting your time trying to contact them.
Role based accounts – Role based accounts (such as sales@, billing@, careers@, etc.) are not very useful for outbound sales efforts. We can detect role based accounts.
Honeypot accounts – There are several initiatives to use honeypot email addresses to catch spammers (for example, Project Honeypot has ~$100M email addresses that they use to detect spam). Although I hate spammers as much as anyone, it is possible for legitimate businesses to acquire honeypot email addresses. Sending an email to honeypot addresses will flag the sender as a spammer and result in being blacklisted. We have technology to detect honeypot addresses.