Check your SMS spam folder

Almost everyone who uses email knows there is a spam/junk folder, and know what it is. We love it. It keeps us sane. But the spam filters occassionally get things wrong. That's why when you sign up for a newsletter you are sometimes presented with a reminder to check your spam folder.

Newsletter preferences form with a reminder to check the email spam/junk folder: If you can't find the message, check your junk folder.

It is common nowadays for SMS messaging apps to also have spam filtering. And similar to email spam filters, it can get things wrong. Yet, I don't see apps reminding users to check their SMS spam folder when sending an OTP to the user's phone.

Not receiving an OTP to access your own account is a frustrating UX. The user feels like they've done everything right and still couldn't get into their account.