reports from places such as spamcop, AOL's feedback loop, and Network Abuse Clearinghouse, the domain's abuse@ mailbox, etc., ISPs can often learn of problems before they seriously damage the ISP's reputation and have their mail servers blacklisted. FROM field control Both malicious software and human spam senders often use forged FROM addresses when sending spam messages. Control may be enforced on SMTP servers to ensure senders can only use their correct email address in the FROM field of outgoing messages. In an email users database each user has a record with an email address. The SMTP server must check if the email address in the FROM field of an outgoing message is the same address that belongs to the user's credentials, supplied for SMTP authentication. If the FROM field is forged, an SMTP error will be returned to the email client (e.g. "You do not own the email address you are trying to send from"). Strong AUP and TOS agreements Most ISPs and webmail providers have either an Acceptable Use Policy (AUP) or a Terms of Service (TOS) agreement that discourages spammers from using their system and allows the spammer to be terminated quickly for violations. Legal measures From 2000 onwards, many countries enacted specific legislation to criminalize spamming, and appropriate legislation and enforcement can have a significant impact on spamming activity. Where legislation provides specific text that bulk emailers must include, this also makes "legitimate" bulk email easier to identify. Increasingly, anti-spam efforts have led to co-ordination between law enforcement, researchers, major consumer financial service companies and Internet service providers in monitoring and tracking email spam, identity theft and phishing activities and gathering evidence for criminal cases. Analysis of the sites being spamvertised by a given piece of spam can often be followed up with domain registrars with good results. New solutions and ongoing research Several approaches have been proposed to improve the email system. Cost-based systems Since spamming is facilitated by the fact that large volumes of email are very inexpensive to send, one proposed set of solutions would require that senders pay some cost in order to send email, making it prohibitively expensive for spammers. Anti-spam activist Daniel Balsam attempts to make spamming less profitable by bringing lawsuits against spammers. Machine-learning-based systems Artificial intelligence techniques can be deployed for filtering spam emails, such as artificial neural networks algorithms and Bayesian filters. These methods use probabilistic methods to