connection_offlinetime verifiedimportantWritten by the Hub
How long a receiver is considered down
After a failed connection or handshake, how long the engine stops trying that receiving address.
In detail
Five minutes by default, and it explains behaviour that otherwise looks like a bug: one refused handshake and the node ignores that server for the next five minutes, even for messages that have nothing to do with the first. It is the right instinct — retrying a server that just refused the handshake is how a sender turns a temporary problem into a reputation one — but it also means a single bad moment shapes the next five minutes of a queue. When a domain has several MX addresses the others carry on, which softens it; when it has one, everything to that domain waits. The Not tried errors counter in the console counts exactly these — messages the engine did not attempt because it already knew the destination was refusing.