BaGoMa backs up and restores the contents of a GMail account. It can restore all the labels (folder structure), as well as the flags (seen/read, flagged) of a message. It supports the use of any character in labels, including non-ASCII characters and "/" (the label hierarchy delimiter). BaGoMa is tuned to work specifically with GMail. Each message is only downloaded and saved once. Backup solutions that are designed to work with regular IMAP accounts will download each message multiple times (once per label) when used to back up a GMail account. This can significantly increase the bandwidth requirements and the amount of storage required for backup. Additionally, a faithful restoration of your GMail account might not be possible from such a backup.
E-MailRelay is a simple SMTP store-and-forward mail transport agent (MTA). It runs as an SMTP server, storing incoming e-mail in a local spool directory, and then forwarding the stored messages to a downstream SMTP server on request. It can also run as a proxy server, forwarding (and optionally pre-processing) incoming e-mail as soon as it is received. It does not do any message routing other than to a local postmaster. Because of its simplicity E-MailRelay is extremely easy to configure, typically requiring only the address of the downstream SMTP server to be put on the commandline.
Enterprise File Exchange (EFX) slots in where email file attachment size limits stop your users from sending files to another person. In the EFX system, the user visits the EFX site, uploads the file, enters the receiver's email address, and lets the system notify the receiver that there's a file waiting for them via a simple email message. The receiver then either simply clicks on the download link provided in the email message or visits the site to download it from there.