An OTP (one-time password) email is a message containing a short code — usually four to eight digits — that is valid for a single use within a limited time window. OTPs are used for login verification, signup confirmation, and two-factor authentication.
How OTP delivery works
When you attempt an action that requires proof of address ownership, the service generates a random code, stores it server-side with an expiry, and sends it to the address on file. You retrieve the code from your inbox and enter it into the form. The service compares what you entered to what it stored; if they match and the code has not expired, the action is authorised.
OTP by email versus OTP by SMS
SMS OTPs are delivered to a phone number; email OTPs to an inbox. Both have the same fundamental property (single use, time-limited) but different threat models. Email OTPs can reach a temporary inbox; SMS OTPs require a real SIM. Email is slower (relies on mail delivery, not instant messaging) but works globally without per-message costs.
Using a temporary inbox for OTP email
This is the single most common use of a disposable inbox. The flow is: copy the address, submit the signup form, watch the inbox, read the code. On EmailGenerator.pro, detected codes are extracted from the message body and shown at the top of the viewer so you do not have to search through the HTML.
Limits to be aware of
OTPs for high-value accounts — banking, government services, payment processors — will not arrive in a temporary inbox because those services block disposable domains. This is by design: high-value accounts should be tied to a durable address you control long-term.