How to Telnet to Pop3 server

They need to relay off of port 587 if they're not already - port 25 is only present on the Default Receive Connector, which doesn't allow client relay like you're trying to do. You can also check the settings of the Client Receive Connector to ensure it matches the settings you're trying to use.

It sounds like you are expecting the POP3 server to receive emails from other providers (eg gmail). POP3 does not 'receive' email. POP3 is purely used for clients (eg Outlook) to connect to a mail server and pick up email stored in a mailbox. Email is delivered from sender to destination entirely using SMTP.

Email works as follows (ignoring stuff like Exchange which has different methods for moving email about internally that we don't really need to know about at this point):

• End user sends you an email which gets delivered to their ISP via SMTP
• ISP's SMTP server looks up your MX records and delivers the email, still via SMTP, to your mail server.
• Your SMTP server receives the email and stores it in your mailbox
• Your email client picks up the message from your mailbox using POP3/IMAP/etc.

I've never used hMailServer but you'll need to set it up as follows if you want it to handle email for your domain.

• Enable the SMTP service and make sure it's working (should listen on port 25)
• Configure hMailServer to handle email for your domain and set up your email addresses/accounts
• Point the MX record for your domain at your mail server
• Enable the POP3 service so you can pick up your emails
• Configure your mail client to connect to hMailServer using the POP3 login details