We have boilerplate text you can use to contact the admin or moderators of a compromised server that's sending spam, available in English, Japanese, and Mandarin: https://docs.google.com/document/d/1z6yZuBcFNMStKBpNg9WGJjkmftZSFSIGvrRGfYvU5RA/
So far over a dozen compromised servers have modified their registration settings and removed any spam accounts and messages, thank you!