On 8/10/26 2:19 PM, Boris Mutina via mailop wrote:
Hello, need advice about greylisting practices. Here's the scenario: - sender at example1.com sends automatic emails using the MTA infrastructure of his provider - recipient at example2.com greylists provider's IP_1 - provider retries from IP_2 which gets greylisted too, again.Tried to dig into RFC6647. Chapter 4.1 describes 'Unintended Mail Delivery Failures', in particular "although example.com has sought to improve its email throughput by having two servers, it has, in fact, amplified the problem of legitimate mail delay introduced by greylisting.". Considering MTA cluster of sender's provider with 4k IPv4 and 2^80 IPv6, the issue grows. On the other hand there are recommendations that recipient at example2.com adopted, except 5.5 which seems to be too risky. This point discusses /24 blocks which is enough risky to "ungreylist" - spammers tend to abuse more than one IP from the /24 blocks. The provider recommends "adjusting anti-spam/greylisting configuration to properly handle messages sent from rotating IP addresses". And I have no clue what does he mean by that. Any advices, opinions? Many thanks.
I use greylisting only when sender fails SPF checks and it's still an effective antispam tool, using it on all mail flow can cause issues like you those you have described above. Giovanni
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