To control spammers,  Wildcat! SMTP offers SMTP authentication which requires that the user login before he is allowed to send mail:

Some users do not have email software that offers SMTP authentication, hence they are not allowed to send mail outside your system..   In addition, it can be a support burden.  Even if the user has SMTP authentication capabilities with their email software, it is typically disabled. So first time users will probably have problems until they are told they need to turn on SMTP authentication.

To address this support issue, a feature called POP BEFORE SMTP was added to Wildcat! POP3 and SMTP servers.

POP BEFORE SMTP works under the idea that the user will be using email software to first connect to the POP3 server to pick up mail before connecting to the SMTP server to send mail..   With this feature enabled, the Wildcat! POP3 will open a "limited time window" which will allow the connection IP access to send mail.   Wildcat! POP3 will give the Wildcat! SMTP server the connection IP and if the user connects to SMTP, the server will allow the user to send mail only within a specific time window.

Enabling POP BEFORE SMTP in Wildcat!

See WCCONFIG | MAIL SERVER | POP3 SERVER setup.