Incoming and Outgoing Mail Servers
The incoming mail server is the server associated with you email address account. There can not be more then one incoming mail server for an email account. In order to access your incoming messages, you need an email client: a program that can retrieve email from an email account, allowing a user to read, forward, delete, and reply to email messages. Depending on your mail server, you can use a dedicated email client (like Outlook Express) or a web browser (like Internet Explorer, for accessing web based email accounts, like Hotmail). The mail is held in storage on the incoming mail server until you download it. Once you have downloaded your mail from the mail server it cannot be downloaded again. In order to download your Email, you must have the correct settings configured in your Email client program. Most incoming mail servers are using one of the following protocols: IMAP, POP3, HTTP.
This is the server used only to send emails (to transport them from your email client program to the receiver). Most outgoing mail servers are using the SMTP protocol (Simple Mail Transfer Protocol) for sending emails. Depending on your network settings, the outgoing mail server can belong to your ISP or to the server where you setup your email account. As an alternative, you can use a subscription based SMTP server (like smtp.com), which will allow you to send emails from any email account you already own. Due to anti-spam reasons, most of outgoing mail servers will not let you send emails if you are not logged on their network. An open-relay server will allow you to use it for sending emails, no matter if you belong to its network group or not, thus it is a heaven for spammers.
eMail Servers and Ports
For networks, a port means an endpoint to a logical connection. The port number identifies what type of port it is. Here are the default email ports for: