Emailrazor deep validation technology, divides emails in 3 groups:
These emails are associated with domains that accept everything that comes in, no matter the destination mailbox exists or not. These domains may have an anti-spam tool that could remove or bounce your email later.
These emails are associated with domains that are known for providing temporary mailboxes that stay just for few hours or few days. Users usually use this kind of services when they want to subscribe to a site or service, but are not interested in getting back info from it on the long run. For example they are used to fill in forms that ask for an email address to send a download link (like: "Subscribe to our newsletter to receive a link to download our white paper on..."). These addresses are "technically" valid (at least for some time), but you don't really want them in your list!
It happens that SMTP servers (the servers which receive emails) report a temporary mailbox error, for example when the mailbox is over quota and can't receive more emails, or block our inspection (usually because of a greylisting policy or a over strict anti spam filter). Email addresses whose SMTP servers show this kind of behaviour, are classified by Emailrazor as risky. Basically they are formally correct but their mail servers didn't confirmed they are deliverable.
Emailrazor assigns a score to each verified email address. This score range from 0.0 (undeliverable because bad format) to 1.0 (good and deliverable). There are a number of factors considered by Emailrazor to assign that score and in general we strongly suggest to not send emails to addresses with a score lower than 0.5, whose are in fact marked as risky.
Our suggestion is to immediately get rid of disposable domain emails and maybe keep all risky emails in a separate list where you can periodically (like once every 2 months) recheck them and see if something changed.
Maybe some temporary errors resolved and some emails regained the status of delivrable, or maybe some of them had been deleted so that you can ditch them out of your list.
In any event, Emailrazor can identify risky emails - and tell you why they are - and empowers you to determine what strategy adopt with them.