smtp bounce code
451 4.4.1Connection timed out
what to do
Retry, do not suppress
The receiving server did not answer. No information about the address at all.
What the server is telling you
The connection was opened and then stalled, or was never completed. Causes range from an overloaded server to a firewall silently dropping traffic from your IP.
Next steps
- →Retry later.
- →If every destination times out, the problem is your connection, not theirs.
- →Outbound port 25 is blocked on every major cloud host, which produces exactly this.
Commonly returned by: Everything
Find these before you send, not after
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