Abuse reports ==
XMPP servers properly compliant with [https:xmpp.org/extensions/xep-0157.html XEP-0157] expose contact addresses for reporting abuse. At the moment, Gajim must be used for sending queries to obtain those addresses; I don't know of any other clients that expose an XML console at the moment.
Paste the following snippet into the console and replace <code>email@example.com</code> with your Jabber ID (JID) and <code>offendingdoma.in</code> with the domain you want to obtain contact info from.
Look at the output and search for this snippet:
<field var="abuse-addresses" type="list-multi">
The addresses in the <code><value></code> tags are who you should contact. <code>mailto:</code> indicates an email address and <code>xmpp:</code> indicates a JID. I recommend just picking one. In either case, contact that address and wait 7 days for an appropriate response before contacting their ISP. If the ISP doesn't take action, open a PR adding that domain to [https:github.com/JabberSPAM/blacklist JabberSPAM/blacklist].