IMAP, POP3 and SMTP: Which Email Protocol Should You Use?

When you set up an email client like Outlook, Thunderbird, or Apple Mail, you encounter three protocol acronyms: IMAP, POP3, and SMTP. Each serves a different purpose, and choosing the right one for your use case affects how your emails sync across devices, how much storage you use, and whether you can access messages offline.

Quick Overview

IMAP vs POP3 vs SMTP: A Side-by-Side Comparison

Before diving into each protocol individually, it helps to see them lined up against each other. The table below compares what each one does, whether it syncs across devices, where your messages are stored, and which ports to use. Understanding these four dimensions makes it much easier to pick the right setup for how you actually work with email.

IMAP (Internet Message Access Protocol)

IMAP is the modern standard for receiving email. It keeps messages stored on the mail server and synchronizes the state (read/unread, folders, flags) across all your devices.

Pros

• Access the same inbox from phone, laptop, and desktop — all stay in sync
• Emails remain on the server — safe even if a device is lost
• Folder structure syncs across all clients
• Works well with webmail simultaneously

Cons

• Requires an active internet connection for full functionality
• Uses server storage (you pay for storage quota)
• Can be slow on high-latency connections for large inboxes

POP3 (Post Office Protocol 3)

POP3 downloads emails from the server to your local device and (by default) deletes them from the server. It's a simpler, older protocol designed for single-device use.

When POP3 Makes Sense

• You only ever access email from one device and want to keep it offline
• Your mail server storage is very limited
• You need a local archive without ongoing server storage costs

SMTP (Simple Mail Transfer Protocol)

SMTP is used exclusively for sending email. IMAP and POP3 handle receiving; SMTP handles sending. Every email client needs SMTP configured to send outgoing messages.

• Port 465: SMTP with SSL/TLS (implicit SSL)
• Port 587: SMTP with STARTTLS (recommended — starts unencrypted, upgrades to TLS)
• Port 25: Server-to-server SMTP. Usually blocked for client use to prevent spam.

Choosing IMAP or POP3 (Sync Across Devices vs Store Locally)

The most common question when configuring an email client is whether to pick IMAP or POP3. The right answer depends entirely on how you use email day to day. Here is a simple way to decide.

Choose IMAP if…

• You access email from multiple devices — phone, laptop, tablet — and want read/unread status, folders, and deletions to stay consistent everywhere
• You use webmail alongside a desktop client; IMAP keeps both perfectly in sync
• You worry about losing mail if a device breaks or a phone is lost, since the real messages stay on the server

Choose POP3 if…

• You only ever use email from one device and want reliable offline access at all times
• Your mail server storage quota is very limited, so downloading messages locally and removing them from the server saves space
• You want a permanent local archive of your email without ongoing server storage

Setting the Correct Ports (IMAP 993, POP3 995, SMTP 465/587)

Choosing the right port matters because using the wrong port — or pairing it with the wrong encryption type — will stop the connection from succeeding. The simple rule is: always use the encrypted port.

• IMAP — Port 993 (SSL/TLS): The standard encrypted port for syncing incoming mail. Use this as your default.
• POP3 — Port 995 (SSL/TLS): The encrypted port for POP3, used when you choose to download mail to your device.
• SMTP — Port 465 (SSL) or 587 (STARTTLS): Both are secure. Port 587 is often recommended because STARTTLS is widely supported, but 465 works equally well where available.

When you configure the account, make sure the encryption type matches the port: ports 993, 995, and 465 use SSL/TLS, while port 587 uses STARTTLS. Mismatching them — for example setting port 993 with encryption set to "None" — will cause the connection to fail.

Port Number Reference

AsiaGB Mail Server Settings

If your hosting is with AsiaGB, use these settings in your email client:

Common Problems (Can't Send, Can't Receive, Ports Blocked by ISP)

When an email client fails to connect, the cause is rarely a server problem — it is almost always a mismatched setting. Work through the most common symptoms below before raising a support ticket.

Can't send email (receiving works, sending fails)

• SMTP authentication is off: Modern mail servers require you to log in before sending. Enable "My outgoing server requires authentication" and use the same username and password as your incoming server.
• Using port 25, which the ISP blocks: Many internet providers block outbound port 25 to limit spam. Switch to port 465 or 587 instead.
• Encryption doesn't match the port: Port 465 needs SSL/TLS, port 587 needs STARTTLS. Pair them incorrectly and outgoing mail will fail.

Can't receive email

• Wrong server name or port: Confirm you are using mail.yourdomain.com with port 993 (IMAP) or 995 (POP3).
• Incomplete username: You must enter the full email address, e.g. [email protected], not just you.
• Quota is full (IMAP): If the mailbox is full, new messages cannot arrive. Delete old mail or increase storage.

Ports blocked by ISP or firewall

If every setting is correct but the connection still fails, an ISP, office firewall, or antivirus may be blocking the port. Test on a different network — for example, a phone hotspot. If it works there, the original network is blocking that port; contact your network administrator or switch the SMTP port from 465 to 587 (or vice versa). In the meantime, webmail over a browser (port 443) is always a reliable fallback.

Frequently Asked Questions

Should I choose IMAP or POP3?

For almost all use cases in 2026, choose IMAP. It syncs across every device and keeps your mail safe on the server even if a device is lost. Use POP3 only if you access email from a single device, need full offline access, or your server storage quota is very limited.

What are the correct ports for IMAP, POP3, and SMTP?

Always use encrypted ports: IMAP on port 993 (SSL/TLS), POP3 on port 995 (SSL/TLS), and SMTP on port 465 (SSL) or 587 (STARTTLS). Avoid the unencrypted ports 143, 110, and 25, which can expose your password and message content.

Why can I receive email but not send it?

This is almost always an SMTP configuration issue: SMTP authentication is turned off, you are using port 25 which your ISP blocks, or the encryption type does not match the port. Switch to port 465 or 587, enable authentication, and use SSL/TLS or STARTTLS accordingly.

Does AsiaGB Hosting support IMAP, POP3, and SMTP?

Yes. AsiaGB email via DirectAdmin supports IMAP, POP3, and SMTP with SSL. You can connect Outlook, Thunderbird, or Apple Mail right away using mail.yourdomain.com as the server.