Validation asks whether an address is well formed and whether its domain is capable of receiving mail. Both are answerable from the outside, cheaply and instantly, and that is what this tool does.
Verification asks whether one particular mailbox exists and will accept a message. That is close to unanswerable remotely. Large providers accept every recipient during the SMTP conversation specifically so that address harvesting cannot work, so a positive response proves nothing. Services advertising real-time mailbox verification are mostly reporting that the domain accepted a connection.
The only dependable verification is sending a message with a link and waiting for the click. Every other method is inference.
The length limits, for the record
These come up constantly in bug reports. RFC 5321 caps the local part at 64 characters and a domain at 255, but the practical limit on a whole address is 254, because that is what fits in the SMTP command carrying it. A database column of 255 characters is therefore sufficient, and a column of 100 is not — real addresses do exceed it.
To dig into just the throwaway question, use the disposable email checker. For the mail routing behind a domain in detail, see the MX lookup.