Phishing for mail account passwords increased in 2008, and typically they were sent from a student's account at an academic institution, where the student had responded to identical spam.
From: "Surname, Forename" <Forename.Surname[at]cit.act.edu.au> (a compromised account)
Subject: mailbox has exceeded the storage limit
Your mailbox has exceeded the storage limit set by your administrator.You may not be able to send or receive new mail until your mailbox size is increased by your system administrator. You are required to contact your system administrator through e-mail with your Username:{ } and Password:{ } to increase your storage limit.
System Administrator
E-mail: system_webincrease[at]live.com
You will continue to receive this warning message periodically if your inbox size continues to exceed its size
limit.This email is intended only for the use of the individual or entity towhich it is addressed and contains
information that is privileged and confidential.
Sysadmins at the institution will usually respond quickly to a report of a compromised account by closing the account or changing the password, so SpamCop is a quick way of doing this. Occasionally it seems SpamCop is able to parse the HTTP submission all the way to the Nigerian ISP, although sometimes it is the abuse address of the institution hosting the compromised account. Of course the same report is not currently also forwarded to the live.com abuse address, which clearly should be notified. This therefore has to be done manually, as described at http://forum.spamcop.net/scwik/ReportingEMailAddresses . So unfortunately SC is not a big time saver in reporting scams where the From and Reply-To address (or From and address that appears in the body) differ.
The decision to not implement an option to report to sysadmins responsible for, e.g. Reply-To address or a single address in the body is understandable if you accept the assumption that all email addresses in spam are forged - but in fact Reply-To and body email addresses in a large fraction of spam are genuine, and the wave of webmail phishing in 2008 changes the situation significantly, as allowing collection accounts to continue for hours or days after a phishing mailout vastly increases the possibility of the inconvenience of a compromised email account, and also of fraud against vulnerable people.
Reporting collection account addresses is analogous to reporting "spamvertised websites" - for example, if a 419 includes a web link it is very likely to a news article on a genuine server. It has to be to the discretion of the reporter to choose which addresses are appropriate to receive the report. Ideally SpamCop itself would make a default decision about whether the type of spam means it could or should be reported to the provider (I have SpamAssassin rules to do this relying on phrases such as "System Administrator E-mail...", but the presence of an account at a free email provider is also evidence).
I think adding the ability to report mailto URIs in the same way as HTTP URIs would be effective and worth a bit of development time.
