NTO has been noting reduced deliverability when they do large sends.

The issue of reduced deliverability tied to hitting spam traps during large email sends is directly related to List Hygiene. Spam traps are often email addresses that are specifically set up by blacklist providers or others to catch spam, and hitting them can severely impact a sender’s reputation. Effective list hygiene practices, such as regularly cleaning the email list of inactive or invalid addresses and confirming the opt-in status of subscribers, help avoid these traps and maintain good deliverability.