Source
The widest reach and the least setup of anything here, and the only source a non-technical sender never has to be told about. We generate an address. What is forwarded to it is the delivery.
The messages sent to the address we generate for this monitor, matched on sender or on a subject line so that a shared address still resolves to the right delivery.
A monitor works from four things about a message: who sent it, its subject, when it arrived, and how big it was.
Nothing installed, and no credential. You forward to the address, or the sender writes to it directly.
One rule for what counts: a sender, a subject, or both.
Healthy - A matching message arrived inside the window, or the window has not opened yet.
Missed - Nothing matching arrived before grace ran out.
Check broken - Rare here, because there is nothing to authenticate against. A forwarding rule that stops matching shows up as a miss, which is the honest reading: nothing arrived.
Four steps, and one test that has to pass before anything is saved.
Common questions: A sender who forgets and uses the old address is the usual failure, and it reads as a miss, because from our side nothing arrived. Matching on subject rather than sender survives a sender changing their address.
Free for 3 monitors. The test has to pass before anything is saved.