When setting up your email program to access your May First Mail, there are two "protocols" to choose from.
Post Office Protocol (POP) means that all of your email is downloaded from your Internet Service Provider to your own personal computer and (usually) deleted from the server (unless you elect to configure your email client to "Leave messages on server"). If you created folders in your email program, those folders are only accessible on your own personal computer.
Internet Message Access Protocol (IMAP) means that all of your email is saved on your Internet Service Provider's servers. If you are using IMAP, you can run an email program at home and an email program at work and both programs will access the same set up messages and folders. If you only use webmail to check your mail, you are using IMAP.
In addition to protocol, there are three main categories of programs you can use to read your email:
Common "desktop" email clients include Thunderbird, Outlook or Mac Mail. These are all programs that are installed on your personal computer. With these programs, you can use either the IMAP or the POP protocol.
In addition, people often use "webmail" clients, such as as Roundcube or Horde (both are available for May First members via the webmail.mayfirst.org site). These are all programs that you access by opening a web browser and going to a particular web page to read your email. Webmail clients are automatically configured for you to use the IMAP protocol.
Most mobile phones come with their own, default email program. As with Desktop clients, when configuring email on your phone, you will be given the option of choosing either IMAP or POP.
Below are three scenarios common to activists. Most likely, one scenario will make sense to you. If not, feel free to contact support with more questions.