Installing LogicMail means that potentially you can have three types of email account on your BlackBerry - push, IMAP and POP.
At the very least, this application allows you to connect to a POP3 or IMAP mail box - with full support for IMAP folders - and send email using SMTP and its various authentication methods.
LogicMail also supports multiple accounts, will display attachments and allow configuration of attachment download sizes.
WiFi enabled phones can take advantage of this connection to connect LogicMail to the internet - other uses may find that they require a generous data tariff with their network/carrier, however.