Could be, but it's more likely that the delete gets put into a message queue and gets processed when the deletion service can handle it. These large deletions are computationally expensive.
Its similar to why the exports take so long to process
You should really start using an email proxy like simple login on anonaddy. I haven't gotten a password reset email in years, and when I do I just change the email and password of the account, then burn that alias.
Both of these sources seem like things that would be blocked by using a DNS sinkhole. I personally use technetium but pihole and adguard are more popular, but less feature rich and harder to set up as a recursive resolver.
The burden of proof is on the accusor