untriederrors verifiedimportant
Not tried — permanent
Messages failed without an attempt, because the engine already knew the attempt would fail.
In detail
MailerQ remembers. A destination that just refused permanently, or a server that just refused a connection, is not tried again for every queued message — the rest are failed immediately with the same reason. connection_offlinetime, five minutes by default, is how long that memory lasts. This is the counter that explains a sudden cliff: thousands of messages failing in one second without any of them touching the network. Read without knowing about it, the graph looks like a catastrophic outage; read with it, it is one failure amplified across a backlog. For our own charts it belongs beside errors but visibly distinct, because the two answer different questions: what the receiver said, and how many messages inherited it.