For example, relaying is turned off by default, as are messages with invalid host names in the return address and unqualified domain names. Instead of sending unsolicited mail from their servers, spammers often relay the mail through another company's server. When the mail arrives at its destination, the origin of the message is then the relay site. This often occurs without the knowledge of the employees at the site being used, and it can cause major hassles such as an overload on the server or legal problems. New features let managers reject all-numeric user names and large numbers of messages sent at one time to numerous users.
Network administrators can also reject messages based on header content.
Sendmail's more difficult task lies not in preaching to those who like tinkering with source code, but in the company's ability to convince businesses to shell out money for a product based on code that has long been free. To that end the company will package a Sendmail 8.9 Pro edition with World Wide Web-based graphical tools for managing and configuri ng servers, binary distributions designed to eliminate the costs of implementing source code releases and support services. Sendmail hopes this approach will take advantage of the trend toward open standards, protect universal access to Internet messaging, and at the same time fend off the dependencies on big vendors' proprietary products. Whether ISPs and businesses buy into the offering remains to be seen. The University of Maryland's Winchester, a Sendmail user since 1985, now manages more than 70,000 user accounts that use Sendmail.