Priorities need to be set for email types.
Each hosting has its own limits, there are specific email hosts that allow you to send a few thousand emails without ending up in spam. But certainly no one allows you to send 55,000 emails at the same time.
For example, I migrated the forum from vb to ipb and I would like to send an email to all subscribers to tell them. Even if it takes me 100 days nothing happens, it's not an important email. At least I can send them for free without having to purchase an external email service.
@Daniel Falternatively, what would you do now to contact 55,000 users? Without ending up in spam and without the hoster blocking my plan?