To get to this page, go to Settings → Legacy Extensions
Legacy Extensions are a way that VPOP3 v2 and earlier could be extended to alter their behaviour. Current installations of VPOP3 should use Scripts or Plugins instead. Legacy Extensions were standalone command-line executable files (EXE files) which VPOP3 ran on certain events and possibly sent data to and received data from to alter its behaviour. These were slow and often unreliable, so the extension mechanisms were altered in later versions of VPOP3, but the options are still available for backwards compatibility.
We do not recommend that anyone use these mechanisms for creating new extensions for VPOP3. Instead use scripts or plugins as appropriate. (Scripts use the Lua scripting language, Plugins are created as Windows DLLs)
If these options are blank, then VPOP3 will skip the extension hook.
•External Router - when VPOP3 downloaded a message using POP3 and was about to deliver it to a user, VPOP3 passes the message content and data about the message (recipient, sender etc) to a program called an 'External Router' program. The output of this program will determine what VPOP3 should do with the message.
•OutMail Pre-processor - when VPOP3 received a message using SMTP, it runs the OutMail Pre-processor program with the message data as input, and receives modified message data as an output. If Run OutMail Pre-processor for incoming/local mail is checked then this program is run for all SMTP messages, otherwise it is only run for messages to external recipients.
•SMTP Client Processor - when VPOP3 is about to send a message out via an SMTP relay Sender, VPOP3 passes the message to the SMTP Client Processor program.
•Post-Connect Command - VPOP3 runs this command just after it makes a Connection to the Internet. This used to be commonly used for triggering other programs to use the same dial-up connection session before the days of always-on connections.
•Pre-Disconnect Command - VPOP3 runs this command just before it disconnects a Connection. This used to be used to tell other software to stop using the dial-up connection which VPOP3 had initiated.