Almost all web servers will have port 25 and/or port 2525 open for sending mail. Usually port 110 is shutdown for receiving mail as there's typically a dedicated mail server - not a web server - for that so you need to be able to support and query pop3 on a remote machine instead of monitoring port 110 locally.

 

Sending mail is something that's pretty common and you can use cdo or cdonts examples found almost everywhere without needing to create a dll. If you want to handle send errors/kickbacks or maintain a "sent mai"l folder though, you may need your own smtp dll.

 

A pop3 receive mail component is not terribly hard to write if port 110 is open. Basically you listen on the port and stream all traffic to a data handler. The RFC is pretty good for documenting the things you need to look for in the steram. The difficulty with the app comes in managing and displaying the received mail.

 

The windows api's for pop and smtp haven't changed substantially in a long time so older vb examples using the win32 api should work for creating a dll.

 

For an example of the pop3 admin and display stuff you'd need to handle, check out JMailBox which uses the JMail component.