Thank you for the feedback. I just sent your code, isitgettingthrough:token:92b930c6-b2ff-419a-ba1d-a8efcd05f100, to the gmail address and it went through--I saw an email from you at the gmail account which went to the inbox but there wasn't a "isitgettingthrough:token:" at the beginning so it didn't detect it. I could make it more visible that the prefix for the token is required. I haven't checked what happened to the outlook email though.

The stuck-in-spam-or-outage can be addressed by me by also checking the spam folder and reporting which box the token got sent to. I could also report on the website that the inbox was last checked without errors at date x (i.e. valid pop3 connection.)

The reputation loss would be very difficult to control; I could whitelist everything that contains that token prefix (i.e. "isitgettingthrough:token:") but then it'd be hard to tell if the provider though it was spam as it would be whitelisted.

The waiting period is dependent upon how many emails I receive from my other accounts (gmail automatically checks them based on a moving average from when the last message was received.) I might be able to change it to email forwarding which could reduce this delay.