POP3 vs IMAP in plain words

If your email shows up on your computer but not your phone, or vice versa, the cause is almost always this. It is not a fault in either device. It is how the two systems work, and it has a simple fix once you know the names.

What is POP3?

POP3 stands for Post Office Protocol, version 3. Its job is to let a workstation retrieve mail that the server is holding for it. The Internet Engineering Task Force's RFC 1939 says that, and adds that normally mail is downloaded and then deleted. Picture a mailbox at the post office: you walk in with your key, take all the letters home and the mailbox is empty. The next person with a key finds nothing. That is why a second phone or computer set up on POP3 sees only new mail that arrived after the first device was done, or nothing at all.

What is IMAP?

IMAP is the Internet Message Access Protocol. Its current version, IMAP4rev1, is described in RFC 3501 as allowing a client to access and manipulate electronic mail messages on a server, with mailboxes acting as remote folders that are functionally equivalent to local folders. Instead of taking the letters home, you read them at the post office and put them in folders there. Every device that connects sees the same folders. That suits a person with a phone, a laptop and a tablet. It also means the server holds your mail, so its size limits and backups matter.

Which one does High Desert email use?

The company's published settings name POP3: incoming mail at pop.hdiss.net, outgoing mail at smtp.hdiss.net, and the username is the full email address. Webmail is at https://hdissmail.hdiss.net/mail/, which shows the mail that is on the server. Whether IMAP is offered, and which ports and encryption to choose, is not published; if your mail app asks for them, call 775-575-9593 or 775-391-5660. The agreement also says email service is limited to High Desert customers and that mail processed by the server must be downloaded to a desktop application, and it makes no promise about mail kept on the server. So treat your downloaded copy as the copy that counts.

Why does mail disappear from one device?

Because the first device to connect took it and told the server to delete it. Most mail apps set up for POP3 have a setting, usually named something like leave a copy of messages on the server, that changes that. With it on, each device downloads its own copy and the server keeps the mail until the app is told to remove it, often after a number of days that you choose. Look in the account settings of the app, under advanced options. The help articles for Outlook, Apple Mail, iPhone and iPad and Android show where each app puts it.

What should I do for a new phone or computer?

Set up the new device with the same incoming and outgoing servers, turn on the leave-a-copy option on both the old and the new device, and let it download. Do not delete the old device's mail until the new one has everything. The guide on keeping email when you change devices covers the move step by step, and backing up your email covers a copy for safety. For a quick look at what is on the server, open webmail from the webmail page.

Should I want IMAP?

If you use more than one device every day, yes, and you can ask the office whether it is offered for your address. If you read mail on one computer, POP3 is fine and keeps your messages in your own hands. Neither is safer by itself; what protects mail is a strong password and a backup. Our guides on passwords and password managers and two-step verification cover that. If you are not a customer yet, the starting point is the address check; a person looks at the path and calls you back.