What a coincidence, we build a FOSS MTA and have a Discourse community ( https://community.kumomta.com/).
Generally speaking the thinking behind greylisting is that botspammers don't bother doing retries, so by issuing a tempfail you get rid of a certain percentage of malicious traffic. I've seen people drop it to a minute when they know they are being greylisted and be fine, but it's certainly something to do while watching closely. Mike Mike Hillyer Co-Founder US Eastern Timezone 443-472-7226 Let's Meet: https://cal.com/mike-kumomta/meet On Wed, Oct 14, 2026 at 11:44 AM Michael Brown via mailop <[email protected]> wrote: > We run a service (hosting Discourse, natch) where we send a *lot* of > email to customers' customers. > > An important chunk of the traffic is email signup verifications — on > initial signup we verify the new user owns the address. Ideally they're > only waiting for a few seconds and can sign up for a forum right away. > Unless their mail server implements greylisting. > > Naturally, this is "our problem to fix" even though delaying mail is a > choice made by the receivers. > > We've kept postfix's five minute default, but is there any kind of > common consensus for a lower value being a safe choice? > > I'm extremely wary of lowering it as we don't want to risk any > reputation damage from aggressive retries, but we also want to provide a > good experience for the end user. > > What do other senders in similar situations do? > > -- > Michael Brown > Civilized Discourse Construction Kit, Inc. > https://www.discourse.org/ > > _______________________________________________ > mailop mailing list -- [email protected] > To unsubscribe send an email to [email protected] >
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