How to Use a Temporary Email Address

The mechanics take about twenty seconds. The judgement about when to use one takes longer, so both are covered here.

The walkthrough

Open the generator. An address is created as the page loads — there is no button to press first.
Copy it. Use the copy button rather than selecting the text; a truncated local part is the most common reason mail never arrives.
Paste it into the signup form. If the form rejects it, the site keeps a disposable-domain blocklist — see why websites block temporary email.
Keep the tab open. The inbox polls every few seconds. Closing the tab does not delete the mailbox, but the browser cookie holding your access token is what lets you back in.
Read the message. Open it in the inbox list; a verification code is surfaced at the top when one is confidently detected.
Finish before the timer ends. Complete the signup while the countdown is still running. Nothing is recoverable afterwards.

Four mistakes worth avoiding

Using it for an account you will keep. The password reset link will one day be sent to an inbox that no longer exists.
Generating a new address mid-flow. A new address is a new mailbox; mail sent to the previous one becomes unreadable.
Waiting on a sender that never sent. If nothing arrives in two minutes, the message was usually rejected at the sender's end, not lost here.
Clearing cookies or switching browser. The access token lives in a cookie. Without it the inbox cannot be reopened, by design.

If the email does not arrive

Check the address you actually pasted, then trigger the send again — the second attempt often succeeds where a greylisted first contact did not. Large senders sometimes queue first-contact mail for a minute or two. If the sender's provider blocks disposable domains, the message never reaches our server at all, and no amount of refreshing will change that.

After you are done

Delete the inbox if you want it gone immediately, or leave it and let the timer handle it. Either way the messages and attachments are removed, not archived.

Questions

Can I extend the inbox lifetime?

Not in this version. Generating a new address is the only option, and it starts an empty inbox.

Can I reply to a message?

No. Every inbox is receive-only.

Will the same address come back later?

No. Once expired, an address is not reissued to you, and any mail sent to it is discarded.