POP3 and IMAP are protocols used to connect your mailbox server to an
email client, including Microsoft Outlook or Mozilla Thunderbird; a
mobile devices such as iPhones and Andriod devices; tablets; and online
webmail interface such as Gmail and Outlook.com.
POP3
stands for Post Office Protocol and has been around for many
years. POP3 downloads your mail as you view it on your email client.
It’s great for users who only want to access their mail from one client.
IMAP
stands for Internet message access protocol and simply connects
to the mailbox and allows you to view your email rather than downloading
it. It is a more modern email protocol and is designed to support our
lifestyles by allowing you to easily view email from multiple locations.
Unlike POP3, your emails will be synced, so if you delete an email in
one client and then check it on an alternate client it will also be
deleted.
Monitoring Your Email Quota
For both protocol types, leaving email on the server counts towards the monthly mail quota on your webhosting account. This may cause delays in viewing email or an interruption in your mail service should your monthly mail quota reach its limit. To prevent your mail quota from being exceeded, you should empty your "trash" folder often to delete messages you no longer want. You should also download any emails that you wish to keep or archive at least once a month.