“Her ISP that allowed SMTP traffic thru their firewall is complicit.” - CV
Please explain
All ISP’s have a firewall. By default you get to go thru their firewall out bound pretty unlimited. But inbound your traffic is highly regulated. The protocol is TCP/IP. Email uses port 25 and has been that way for ever. Your ISP isn’t going to let you set up an email server behind their firewall. Most ISP’s will give you an account on one of their email servers for free. But to have your own email server will cost extra. At minimum the ISP HAS to know you are getting traffic on port 25.