Email verification tests are easy to underestimate. The browser clicks the signup button, a message is sent, and the test waits for it. When the inbox is slow, though, the whole workflow can become a vague ten-minute argument with a timeout.
I like treating this as a small reliability problem instead of a special email problem. A test has a limited amount of time and retry capacity. That is its failure budget. Once the team writes the budget down, an intermittant check becomes easier to explain and less expensive to maintain.
This applies whether the test uses a temporary inbox, a sandbox mailbox, or a helper that creates an address for each run. Even a quick search for a temp mail for facebook test account can lead to the same engineering question: what evidence proves that this run used the right inbox and waited for the right message?
The hidden cost of waiting for email
An inbox check usually has three clocks:
