Marlin from Minneapolis writes:
With Thunderbird (or any other client based email), once it is downloaded to your computer from the mail server is it then deleted and no longer in existence?
E-Mail Clients like Outlook, Windows Live Mail and Thunderbird (along with others) offer a vast array of extra features, but can pose problems if you want to keep your e-mails portable. This is why there are a few different kinds of e-mail systems companies can use – and which one you have access to will determine whether your messages get erased from the server once you download them, or kept accessible for other devices/computers.
POP/POP3: (Post Office Protocol) This is the e-mail method most companies used years ago and many still offer. It will store your e-mails on the server until you download them. In most cases, once you download them they are deleted.
IMAP: (Internet Message Access Protocol) This is the e-mail method prefered by most e-mail providers today and lets your e-mail client sync up to the server and download copies of the messages. This method also lets you access messages on multiple devices and allows them to sync so that e-mails deleted on one device delete on the other and e-mails downloaded on a phone (for example) will automatically download on your other devices next time they connect.
Exchange/Blackberry/Other Corporate E-mail Systems: These e-mail systems most often work very much like IMAP, but support various corporate security systems which prevent access and can control (very specifically) what and how things are sent. They often also support automatic archiving of messages for legal compliance, so even “Deleted” e-mail is often kept for months, sometimes years, based on the company’s requirements. These systems offer multiple device sync and store messages on the server also, and usually require access either through a company IT department or by special request.
What’s the best one to use? IMAP if you have personal e-mail, and Exchange if your using company e-mail – but check with your company as individual configurations can vary greatly.
P.S. Your web based e-mail clients (like Yahoo, Gmail, Hotmail and iCloud all support IMAP as the preferred connection type. You only need to set the connection type if your using these e-mail providers in a dedicated e-mail application the website will automatically save and store your information on the server.