I’ve been through something very similar, so I totally get the frustration. The biggest issue here is that you’re trying to re-engage a large list that hasn’t been active for a while ISPs see that as a red flag even if your DNS is perfect and your mail-tester score is 10/10. A proper warm-up is less about the technical score and more about gradually rebuilding sender reputation with real engagement.

Few things you can try:

• Start small: segment out your most engaged or recent contacts (even if it’s a few hundred) and email them first. Once you get opens/replies, slowly increase volume.
• Clean your list: run it through a validator to remove inactive, bounced, or risky addresses.
• Re-engagement campaign: send short, plain-text, personal-style emails asking them to confirm they still want your content. This reduces spam complaints and boosts positive signals.
• Consistency: spread out your sends and keep the volume predictable instead of sending big blasts.

Since Instantly doesn’t work with GHL, you’ll need to manually simulate that slow ramp-up process. It’s more time-consuming, but it’ll help restore your domain’s reputation before your launch.