IMAP vs POP3: which should you use for business email?

Priya runs a small consultancy and reads email on three devices. When she first set up her mailbox she used POP3 on her laptop, which downloaded every message and removed it from the server. Her phone, set up later, then showed an almost empty inbox, and replies she wrote on the laptop never appeared anywhere else. She spent a week wondering where her messages had gone.

She switched all three devices to IMAP. The mailbox now lives on the server, and each device shows the same inbox, the same sent folder and the same read and unread marks. When she deletes a message on her phone it disappears from the laptop. When she files a client email in a folder, the folder appears everywhere.

The cost of this arrangement is that her mailbox size now matters, because everything is kept on the server. She sets a reminder each quarter to archive old messages into a local folder on the laptop, which keeps the server mailbox comfortably inside its limit. The change took about twenty minutes, mostly spent removing and re-adding the account on each device.

The most common complaint is that devices disagree about what is in the inbox. Nearly always the cause is that one device is still set up with POP3, which pulled the messages away. Check the account type on each device and change any POP3 account to IMAP.

The next most common is a mailbox that stops receiving mail because it is full. Under IMAP, old messages stay on the server until you remove them, so large attachments build up over time. Delete or archive big messages, and empty the trash and spam folders, which count towards the limit.

If a device cannot log in, check the username is the full email address, the password is current and the server name, port and encryption match the settings shown in your control panel. If it connects but sending fails, the outgoing SMTP settings are usually the culprit, since they are set separately from incoming mail.

• Different inboxes on different devices: change any POP3 account to IMAP
• Mailbox full: archive large messages and empty trash and spam
• Cannot log in: use the full address as the username and re-enter the password
• Can receive but not send: check the outgoing SMTP server, port and encryption
• Folders missing on one device: refresh or re-subscribe to the folders in the mail app
• Duplicate messages after a switch: let the first sync finish before changing anything else

For almost everyone today the answer is IMAP. If you read mail on more than one device, if you use webmail at all or if you want your mail to survive the loss of a laptop, IMAP is the sensible choice. It is the default in most modern mail apps for good reason.

POP3 still has a narrow use. It suits a single computer that is the only place you ever read that mailbox, where you want a local copy that does not depend on server storage, or where the mailbox quota is very small. Even then, set it to keep a copy on the server for a few days, so a failed disk does not take your only copy with it. Whichever you pick, you can change later, but do it carefully and with a backup in hand.

Because IMAP leaves mail on the server, mailboxes grow over time, and they count towards your plan's disk space. A busy mailbox with years of attachments can become several gigabytes.

The cure is simple housekeeping. Delete large attachments you no longer need, empty trash and junk folders, and move old mail into a local archive on your computer when you want to keep it but not on the server. Most mail apps let you create a local archive folder that is not synced.

If many people share one hosting account, check mailbox sizes now and then, or choose a larger plan. Remember that email accounts are unlimited on every plan, and space is the thing to watch.

Always use the encrypted version of whichever protocol you choose. Encryption stops anyone on the network between you and the server from reading your password or your messages. Our hosting shows the correct secure settings for your domain, so follow those and avoid unencrypted alternatives.

Use a strong, unique password for every mailbox, and turn on two-factor login on webmail if it is available. A stolen mailbox password gives an attacker a way to reset passwords on many other services, so email deserves the most careful protection of any account.

If you have used POP3 for years, you may have a large archive stored only on one computer. Before you switch, make a backup of that archive. Then add the account again as IMAP, and copy your old messages into folders that sync to the server if you want them available everywhere.

Do it in stages if the archive is large, and keep an eye on mailbox size. For long-term storage that you rarely need, keep a local archive file on your computer, and keep your active mail on the server.