POP3 and SMTP are two different protocols used for passing mail messages between mail machines. Both use the Client/Server principle.
A Client initiates a connection with a Server, then issues requests, which are fulfilled by the Server.
A Server runs continually, awaiting connection requests from a Client. When these arrive, it fulfils them.
The server can, if required, use authentication to decide whether connections from a particular Client should be accepted.
POP3 - Post Office Protocol - Collecting Mail
POP3 is a method of mail collection and always uses authentication: MailCOPA initiates a connection with a POP3 Server, sends the mailbox name and password, then makes requests regarding the download of messages. Usually this will be an automated process, where messages are downloaded, then deleted from the server, but other methods can be used, see Specialised Mail Collections.
MailCOPA uses its own SMTP client for sending messages out. In this instance the distant SMTP server acts as a relay, or smarthost - it accepts the mail, identifies how it should be routed, then passes it on to its final destination.
MailCOPA's SMTP client contacts a SMTP server (typically one provided by your Internet Service Provider, but it maybe on your company intranet), and requests to send outgoing mail, which is then passed to the SMTP server.
You cannot usually use a SMTP relay other than that provided by your ISP: it will reject connection requests from connections identified as not belonging to that ISP, eg if you connect from home rather than work or from a friend's house or a hotel room. This is so as to be able to identify the originator of the mail (in the event of subsequent legal proceedings or misuse contrary to the IPS's terms), and to prevent the forwarding of UCE (Unsolicited Commercial email) often know as spam.
Some servers require that you collect (or attempt to collect where there is no mail waiting) mail first and only then will it allow you to send via it. The principle is that once you authenticate via POP3, it is pretty certain that it is still you trying to send within a short time using the same IP Address. The usual sequence is Send then Collect, but this can be reversed in MailCOPA's Preferences here.
Some servers use a primitive form of authentication (see the paragraph above), but the SMTP protocol also supports the use of formal authentication, which can be used to identify users if they are not connected via the ISP's own connection point. A username and password can be sent along with the initial request for a SMTP connection.
MailCOPA supports SMTP authentication, as described in the User Details (Outgoing tab).