It’s not easy to recover the domain reputation if you don’t change your data acquisition and sending practices. There is a lot of work you need to do to recover a bad domain reputation at Gmail, Hotmail or any other provider, in particular:
- make sure you are practicing a good list hygiene;
- remove bad data from your list;
- target the right people;
- start with a low email volume and increase it slowly every time you have a decline in your reputation;
- make sure you have SPF, DKIM and DMARC records set up on your domain;
- make sure your legal messages pass the DMARC authentication.
It can take anywhere from 30 to 60 or 90 days. It depends on how bad the reputation was but you should start seeing an improvement in 30 days approximately.
Here is a good article for more information: How to Restore Sender Reputation and Get out of the Spam Folder