IMAP vs POP3 vs SMTP: what each email protocol does
IMAP, POP3 and SMTP are not rivals. Learn which one receives mail, which sends it, when POP3 still makes sense, and which settings to pick.
Setting up an email app throws three acronyms at you and asks you to choose. Most people guess. They aren't three competing options. SMTP does one job, and IMAP and POP3 do another. You choose one from the second pair and always need the first.
The one-minute version
- SMTP sends mail. Always needed.
- IMAP reads mail and keeps it on the server, so every device sees the same thing.
- POP3 downloads mail to one device, usually removing it from the server.
If you take one thing away: use IMAP for receiving unless you have a specific reason not to.
SMTP: the sending protocol
SMTP stands for Simple Mail Transfer Protocol. When you press Send, your email app uses SMTP to give the message to your mail server. That server then uses SMTP again to pass it on to the recipient's server.
Your app needs SMTP settings even if it never receives anything. The standard setup is port 587 with STARTTLS, your full email address as the username, and the mailbox password. Port details are in SMTP and IMAP ports explained.
IMAP: the syncing protocol
IMAP is the Internet Message Access Protocol. Your messages stay on the server, and your devices show a live view of them. Read a message on your phone and it's marked read on your laptop. Delete it on the laptop and it disappears from the phone. Folders such as Sent, Drafts and Trash match everywhere.
IMAP also lets you search on the server and download only message headers first, so a big mailbox opens quickly on a slow connection. The standard port is 993 with SSL/TLS.
The trade-off is storage. Everything lives on the server, so the mailbox has to be large enough for what you keep, and old mail is only as safe as the server's backups.
POP3: the download protocol
POP3, the Post Office Protocol, was designed for a time when people dialled in, grabbed their mail and went offline. It copies messages to one computer and, by default, deletes them from the server.
That makes it simple and cheap, and it breaks the moment you have a second device. A message downloaded by your laptop never reaches your phone. Reading state and folders don't sync, because the server doesn't know about them.
POP3 still makes sense in a few cases:
- One computer that reads the mail, and nothing else
- A mailbox with tight storage that you want to keep empty
- An archiving tool that collects mail for storage
Even then, many apps can leave a copy on the server for a number of days, which softens the problem. The ports are 995 for SSL/TLS and 110 with STARTTLS.
Side by side
| SMTP | IMAP | POP3 | |
|---|---|---|---|
| Job | Send | Read and sync | Download |
| Mail stays on server | Not applicable | Yes | Usually no |
| Several devices | Not applicable | Works well | Poorly |
| Common port | 587 | 993 | 995 |
Which should you pick on a phone and laptop?
IMAP. If you read mail on more than one device, you want the same inbox everywhere. Add the account on the phone, add it on the laptop, and both stay in sync. Our phone setup guide shows the exact boxes to fill in.
What about webmail?
Webmail is a third way to read mail, and it doesn't involve any of these settings on your side. A browser talks to the mail service, which reads the mailbox for you. Mailions has private webmail where you sign in with the mailbox address and password. Under the hood it reads mail from the server with IMAP, which is another reason IMAP is the natural choice for everything else: the browser and your apps look at the same mailbox.
Common confusions
"My app asks for an incoming server and an outgoing server." Incoming means IMAP (or POP3). Outgoing means SMTP. They often use the same host name but are configured separately.
"I can receive but not send." The SMTP settings are wrong. Check that authentication is turned on and the port is 587.
"Sent messages don't show up on my other device." With IMAP, your app should save a copy in the server's Sent folder. If it stores copies locally, find the account setting that says where to keep sent items.
"Everything disappeared from my phone after I set up my laptop." The laptop used POP3 and removed the messages from the server. Switch the laptop to IMAP, then recover from the laptop's local copy.
Putting it together
For a custom domain mailbox, use IMAP on 993 for incoming and SMTP on 587 for outgoing, both with the full address and the mailbox password. The mailbox setup guide lists the host name for Mailions. If you want a mailbox on your own domain, contact us.
Frequently asked questions
What is the difference between IMAP and SMTP?
SMTP sends mail: your app uses it to hand messages to a server, and servers use it to pass mail to each other. IMAP reads mail: it lets apps view and organise messages that stay stored on the server.
Is IMAP better than POP3?
For most people, yes. IMAP keeps every device in sync and leaves mail on the server, where it can be backed up. POP3 downloads mail to one device and suits only offline use or very small server storage.
Do I need both IMAP and SMTP settings?
In an email app, yes. IMAP (port 993) handles incoming mail and SMTP (port 587) handles outgoing mail. They often share the same server name and login, but they are configured separately.