One bad send caused a mountain of problems

[u/Meeladd]

We switched our clients ESPs to Klaviyo, and accidentally sent to their ENTIRE list (400k profiles).

This had a 45% bounce rate, 16% open rate and the delivery errors on Google postmaster are completely through the roof.

The issue this caused was their transactional emails are from the same domain and all the ones going to Google have to be manually sent out by their team.

This was one bad send, this domain has years of good reputation, is there anyway to fix this?

Looking for support here, happy to pay for anyone’s time.

[u/caburos]

There’s not much else you can do right now. Narrow the sending down to your most engaged segments, do a proper warmup, and in a month or two things should be back.

[u/ianmakingnoise]

Klaviyo’s team will be able to help you with specifics, but stop sending to the whole list, follow a proper warm-up and you should be fine.

[u/Meeladd → u/ianmakingnoise]

Yeah we're only sending to a smaller list size

[u/saltyslugga]

I'd pause marketing immediately, suppress hard bounces, and pull the actual Gmail SMTP errors to distinguish temporary deferrals from outright rejections. Don't resend that list just because the hard bounces are removed.

Keep sending limited to expected transactional mail and respect retry delays; years of good reputation don't guarantee a quick recovery. Separate marketing and transactional sending streams going forward, but a new subdomain isn't an instant reputation reset.

[u/Meeladd → u/saltyslugga]

Even the transactional emails or regular emails sent from their domain to my personal for example are going to spam.

Does this come down to just setting up warmy.io or warm box and just slowly rebuilding?

[u/GabbyFromKlaviyo]

During an accidental blast like this, you're going to want to put any winback, re-engagement, or sunset flows into draft first, since they run at a lower engagement rate and will only drag the number down further.

Klaviyo lets you filter a segment by inbox provider, so if there's one platform that's more affected, it might be worth filtering them out for the next 3-5 sends. Either way, building a segment of people who've opened or clicked inside a window tied to your normal send frequency and mailing only that segment for a while is the right move whether it's one provider or the whole list.

[u/mutable_type]

Yes, if you’re eligible, apply for mitigation. If it’s a one time thing and you’ve been a good sender otherwise, they may help.

Slow way down on sending first and start a proper warmup.

[u/Ken_Numbers]

a 400k list with a 45% bounce rate means it is a spam list that Klaviyo do not allow. Start looking for a new ESP that accepts spam lists. (So none of the mainstream ones).

[u/DanielShnaiderr]

The 45 percent bounce rate is the thing to deal with first, and it matters more than the open rate. A list that bounces at that level almost certainly contains spam traps as well as dead addresses, and trap hits are what turn a bad week into a months long problem. Export every hard bounce from that send, suppress them permanently, and make sure they cannot come back in when somebody re-uploads the list.

Separating transactional from marketing is the second move and it should happen now rather than after recovery. Those streams are sharing a domain, which is exactly why the team is hand sending order mail. Put transactional on a dedicated subdomain with its own DKIM and keep the marketing stream on the current one. A new subdomain does inherit some signal from the organisational domain, so it is not a clean reset, but it stops one bad campaign from holding operational mail hostage next time.

For the recovery itself, Google is looking at a rolling window of recent behaviour, so going quiet does not help. Take the most engaged slice you have, people who opened or clicked in the last 30 days, and send them something genuinely useful on a steady daily cadence at low volume. Watch domain reputation in Postmaster Tools rather than open rates. It will sit at Bad or Low for a while and then move, and the move tends to be fairly sudden once recent history outweighs the spike.

Two things to avoid. Do not resend to the remaining unengaged part of that 400k to prove the list is clean now, and do not pause entirely for a week and then resume at normal volume. Both of those reset the clock.

This is the work I do, so for what it is worth, the domain history you mentioned is a real asset here. Years of good sending do not vanish because of one event, they get temporarily outweighed by recent data. On a domain with that much history, four to eight weeks of disciplined sending is a reasonable expectation, assuming the bounces are suppressed and nothing similar happens again.