On 2022-11-23 10:39, Cyril - ImprovMX via mailop wrote:
Blocking the recipient had the effect that we don't accept emails for them anymore, so anyone sending an email via ImprovMX to one of their domain will have a 5xx response on the RCPT command. That was our initial strategy, the default when we block an account: we let the sender know the email wasn't accepted.But in this case, I realized one thing: It's possible that the sender could retry, increasing the number of connections at every new bounce. So I've updated the policy on this specific account to accept but silently drop any emails for them.
Silently dropping the mails seems like a bad strategy to me. That would mean you accept DATA and waste your bandwidth and processing power on those. If there was no reaction on you returning a 5XX then my strategy would be to return a 4XX. If the 70K connections per minute actually translates to 70K unique emails per minute then a defer queue rising by 70K per minute should be at a scale that I expect gets noticed even by Microsoft.
-- BR/Mvh. Dan Malm, Systems Engineer, One.com
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