For IP warming, is it critical that we send up to the weekly limits by domain? For example, see screenshot below. Notice each day as the max limit. What if the customer only has a grand total 40,000 Yahoo email subscribers?
Recently had a similar implementation (surprisingly even similar amount of Contacts) and based on my discussions with Salesforce Success Manager and Salesforce Deliverability Team, you do not need to do an IP warm-up at all.
There are a couple of points to know here though. If there was a SAP configured with shared IP, then you're clear. Nothing to do or worry about.
However if you got a private IP (which is standard) then you should avoid creating surprise spikes during Email sendouts.
What it means is if the daily rate is around 400-900 Emails for an example, then you should not do a send to 25000 subscribers without proper planning.
Request Salesforce Service Team to enable Send Throttling on the MC account and during large volume sends simply set some hourly/daily throttling on how many will be processed at once.