Set Up POP, IMAP or Forwarding
Manage multiple e-mail accounts using forwarding, POP3 or IMAP. Google suggests using IMAP. It's up to you which methods you choose to manage your e-mail accounts.
You can configure other e-mail clients to synch with Gmail. Google provides IMAP configuration instructions.
Using Rebelmail with Lotus Notes
What is the difference between POP3 and Forwarding and which should I use?
If you select the forwarding option in your new Rebelmail account, you can forward a copy to an alternate e-mail of your choice. You may also elect to keep or archive a copy in your Rebelmail account, or have it deleted after forwarding. This would be the preferred option if you do not wish to check your Rebelmail account directly.
POP3 is an Internet standard protocol for retrieving e-mail from a server. Setting up a POP3 connection from within your Rebelmail account to a secondary e-mail account will let you retrieve mail from that other account directly into your Rebelmail inbox. You can also set up a POP3 connection with your preferred e-mail client such as Microsoft Outlook or Mozilla Thunderbird so that your messages are downloaded from the Rebelmail server directly into that application. So setting up a POP3 connection is a preferred option for those who wish use their Rebelmail account as their primary e-mail account while maintaining the ability to access mail from secondary e-mail accounts.
Let's say you have a Hotmail account that you have used for years but you would prefer to switch to Rebelmail. You can add your hotmail account to your Rebelmail powered by Google account using a POP3 connection (that way you won't need to log in to two accounts everyday). When a message arrives into your Rebelmail inbox from Hotmail, Google will label it so that you know it came from Hotmail. When you reply, it can look like it's coming from your firstname.lastname@example.org account, instead of your email@example.com account.
What is the difference between POP3 and IMAP?
POP3 and IMAP are both Internet protocols for accessing e-mail messages. POP3 will download a copy of your messages to your local computer from the mail server, but in many cases will not maintain a copy of the messages on the server. IMAP allows you to view the messages on your local computer or mobile device, but the messages are still stored on the mail server. IMAP is the preferred protocol when using e-mail clients (Outlook, Thunderbird, etc.) or mobile devices (Android, iPhone, BlackBerry, etc.) because of better synchronization capabilities and easier accessibility from multiple devices.
If you would like to retrieve mail from a secondary e-mail account directly into your Rebelmail account, and you typically check your mail using an Internet browser, then a POP3 connection is fine for this.
Google describes the difference between POP and IMAP