​@artichoke hey, sorry for your trouble!

Without going into too much technical detail (I’ll let support help you with this), I would recommend excluding your BT contacts from all of your ongoing sends (campaigns and flows), checking that list separately for bounces (via platforms like Neverbounce or something similar) and cleaning it up, and then slowly reintroducing the remaining contacts into your sending cadence.

BT contacts have been the lowest quality list members for most brands I’ve personally audited in recent months and their overall value remains low even without deliverability issues - this is just for your future reference in terms of acquiring these leads.

Let me know if this helped, happy to chat further!

Hi artichoke, I’ve seen this happen with BT addresses before they’re one of the stricter ISPs in the UK when it comes to filtering. A few things that usually help:

• Check your sending domain authentication – make sure SPF, DKIM, and ideally DMARC are properly set up. BT tends to be extra sensitive to missing/incorrect records.

• Prune unengaged BT subscribers – if a big chunk hasn’t opened/clicked in months, that hurts your sender reputation with BT specifically.

• Segment BT users into a smaller list and warm them up gradually with lighter sends instead of blasting the full list.

• Keep content clean – avoid heavy images or spammy words, since BT’s filters are notoriously aggressive.

If Klaviyo support has confirmed it’s not just a temporary issue, working on domain authentication + segmenting usually moves the needle.

If you’re still running into deliverability issues after trying this, I’d be happy to walk you through some setup fixes that have worked for me, kindly reach out to my mail blessingumokuye@gmail.com.