Mistakenly sent mass email with wrong domain, killing its SEO.. how to recover?

I own a few e-commerce websites, and 3 weeks ago I sent 140k emails using the wrong domain name (mixed between 2 businesses). It literally killed its domain reputation within 24h.

SEO, which was not doing good in the first place anyway, dropped to nearly nothing : over thousands of daily visits, less than 1% are coming from organic search.

How can I fix that and recover its domain reputation?
Will buying backlinks on BHW help? Which ones?

How to get emails to be received again? Everything end up in the spam folder now, which was not the case before (legit website).

Detailed answers would be much appreciated! I don't want to do more mistakes and would like to recover the domain reputation

Damn that sounds brutal

Hello,

I'm in this business since years,

You can use a trusted email marketing and use warm-ups ips and all of your emails will be sent to inbox again.

Also you need to stop sending emails for marketing purposes.

It's not wrong , But if you send it with alot of bounces you will be warned from google.