I ran into this ten years ago when I had just retired and started traveling full time, trying to use mailing lists to keep up with family and friends.
I remember first hitting the limit on number of addressees per send, so I split my lists and sent the same thing to two or three lists separately. Then if I sent too many things to too many people, I ran into other anti-spams limits.
I particularly remember shifting my mailing lists from using AOL to send, to Yahoo, because Yahoo had looser limits (and AOL back then was the big target for hijacking accounts for spamming, since AOL mail was still bigger than the Internet).
I don't think you'll be getting anybody's actual numbers, on these limits. The limits change as the big mail services have to adjust to the changing problem, and publishing the limits is simply telling spammers and abusers how to get around them.
People on my mailing lists eventually started pushing me toward social media, starting with MySpace and for my friends in China, an experimental system built by Microsoft to test the concept before jumping in. Then it was something on Yahoo, and most recently FaceBook, which my family has now stayed with (except the youngsters exchanging photos and videos instead of blog-like posts).
If your messages are short, Twitter works very well, can go out to mobile phones almost immediately, but you have to get the interested people to subscribe to your tweets.
Tom Test
Itasca Spirit 29B
