Guide
IMAP vs SMTP: What's the Difference?
IMAP vs SMTP comes down to direction. SMTP sends email; IMAP retrieves it and keeps every device in sync. Your mail app needs both, which is why it asks for an incoming and an outgoing server. Here's how they differ from POP3, and which ports to use.
- Server
- imap.gmail.com
- Port
- 993
- Security
- SSL/TLS
- Server
- smtp.gmail.com
- Port
- 587
- Security
- STARTTLS
POP3 instead? pop.gmail.com · 995 · downloads to one device
Basics
IMAP vs SMTP: the short answer
SMTP is the postal service: it carries a message from your app to your provider and on to the recipient's server. IMAP is the key to your mailbox: it lets any device open, file and search mail that has already arrived.
| SMTP | IMAP | |
|---|---|---|
| Full name | Simple Mail Transfer Protocol | Internet Message Access Protocol |
| Job | Send and relay email | Read and sync email |
| Direction | Outgoing (push) | Incoming (pull) |
| Who talks to whom | App to server, and server to server | App to your own mailbox server |
| Standard ports | 25 (relay), 587, 465 | 143, 993 |
| Current spec | RFC 5321 | RFC 9051 (IMAP4rev2) |
The path of one email
SMTP pushes the message out. IMAP lets each of the recipient's devices read it.
Notice that SMTP appears twice. Your app submits the message to your provider on port 587 or 465, after signing in. Your provider then relays it to the recipient's server on port 25, finding that server through the domain's MX record. The recipient never touches SMTP: their phone and laptop read the message with IMAP, and because IMAP leaves it on the server, both devices see the same folders and the same read status.
Three protocols
IMAP vs POP3 vs SMTP
POP3 (Post Office Protocol version 3) is the older way to receive mail. Like IMAP it reads your mailbox, but it was designed to download messages to one device rather than keep them on the server.
| Mailbox job | SMTP | IMAP | POP3 |
|---|---|---|---|
| Sends mail from your app | Yes | No | No |
| Relays mail between servers | Yes | No | No |
| Reads mail from your mailbox | No | Yes | Yes |
| Designed to keep mail on the server | No | Yes | No |
| Syncs read status across devices | No | Yes | No |
| Works with folders, not just the inbox | No | Yes | No |
| Searches mail on the server | No | Yes | No |
| Standard ports | 25, 587, 465 | 143, 993 | 110, 995 |
Mailbox jobs each protocol handles
Count of “Yes” cells in the table above, out of 7 jobs. SMTP and IMAP do different halves of the work; POP3 does a narrow slice of IMAP's.
| IMAP | 5 of 7 |
|---|---|
| SMTP | 2 of 7 |
| POP3 | 1 of 7 |
POP3 vs SMTP
These two are often confused because old setup screens paired them: POP3 for incoming, SMTP for outgoing. They never overlap. POP3 downloads what's in your inbox; SMTP sends what you write. POP3 clients can leave a copy on the server, but RFC 1939 itself says that normally mail is downloaded and then deleted, and Microsoft notes that POP3 clients remove downloaded messages by default. Changes on one device never reach another. Google sums it up: IMAP syncs in real time across devices, POP is for a single computer.
Ports
SMTP ports, IMAP ports and POP3 ports
Each protocol has a cleartext port that upgrades to encryption with STARTTLS, and an implicit-TLS port that is encrypted from the first byte. RFC 8314 recommends implicit TLS for mail clients where it's available.
| Port | Protocol | Encryption | Use it for |
|---|---|---|---|
25 | SMTP relay | STARTTLS when both servers offer it | Server-to-server delivery. Often blocked for client connections by ISPs and hosts. |
587 | SMTP submission (RFC 6409) | STARTTLS | Sending from a mail app or script. The default for Microsoft 365 and Outlook.com. |
465 | SMTP submission (RFC 8314) | Implicit TLS | Sending from a mail app. Gmail accepts it; Microsoft 365 doesn't. |
2525 | SMTP (unofficial) | STARTTLS | Not an official SMTP port. Some sending services, such as SendGrid, accept it alongside 25 and 587. |
143 | IMAP | STARTTLS | Legacy and internal servers. Prefer 993. |
993 | IMAP (RFC 8314) | Implicit TLS | Reading mail in any client. Gmail, Outlook.com and Microsoft 365 all use it. |
110 | POP3 | STARTTLS (STLS) | Legacy. Prefer 995. |
995 | POP3 (RFC 8314) | Implicit TLS | Downloading mail to a single device. |
Can't send, but receiving works?
Settings
Gmail and Outlook IMAP and SMTP settings
The incoming and outgoing servers for the three most common mailboxes, from each provider's help pages (October 2026).
| Provider | IMAP (incoming) | POP3 (incoming) | SMTP (outgoing) |
|---|---|---|---|
| Gmail & Google Workspace | imap.gmail.com · 993 · SSL/TLS | pop.gmail.com · 995 · SSL/TLS | smtp.gmail.com · 587 STARTTLS or 465 SSL/TLS |
| Outlook.com / Hotmail | outlook.office365.com · 993 · SSL/TLS | outlook.office365.com · 995 · SSL/TLS | smtp-mail.outlook.com · 587 · STARTTLS |
| Microsoft 365 | outlook.office365.com · 993 · SSL/TLS | outlook.office365.com · 995 · SSL/TLS | smtp.office365.com · 587 · STARTTLS |
Every one of these needs authentication on both connections. Google and Microsoft both steer apps toward OAuth sign-in rather than a plain password, in Gmail IMAP has to be enabled under Settings › Forwarding and POP/IMAP, and in Microsoft 365 POP3 and IMAP4 are on by default but switched off automatically if your tenant uses security defaults. Sign-in options, sending limits and error codes are covered in full in the Gmail SMTP server settings and Office 365 SMTP settings guides.
Choosing
IMAP or SMTP: which one do you need?
You rarely pick one. What you're building decides which protocols get used.
| You're setting up… | Protocols | Why |
|---|---|---|
| Email on your phone and laptop | IMAP + SMTP | IMAP keeps both devices in sync; SMTP sends your replies. |
| A website form, printer or app that only sends | SMTP | Nothing needs to read a mailbox. |
| A script that processes incoming mail | IMAP | It reads and files messages; replies, if any, go out over SMTP. |
| An archive of mail on one computer | POP3 + SMTP | POP3 downloads everything locally. |
| A cold email tool | SMTP + IMAP, or OAuth | It sends the sequence and watches for replies. |
How cold email tools use IMAP and SMTP
Step 1
Connect the mailbox
By OAuth (Google, Microsoft) or with IMAP and SMTP details and an app password.
Step 2
Send over SMTP
Each step of the sequence goes out from your mailbox, about 30 a day per mailbox in Jetmail's planning.
Step 3
Watch over IMAP
The tool checks the inbox for replies and bounces.
Step 4
Stop on reply
A reply ends the sequence for that contact so nobody gets a follow-up after answering.
OAuth is the cleaner route where your tool supports it: there's no password stored in the tool and no port to get wrong. Jetmail mailboxes connect to outreach tools this way. See how it works with Instantly and Smartlead, or browse the Google Workspace mailboxes themselves.
Skip the server settings entirely
Jetmail sets up Google and Microsoft mailboxes, domains and DNS, then connects them to your outreach tool by OAuth. No ports, no app passwords.
Sources (checked October 2026): RFC 5321 (SMTP) · RFC 6409 (message submission, port 587) · RFC 8314 (implicit TLS: 465, 993, 995) · RFC 9051 (IMAP4rev2) · RFC 1939 (POP3) · Gmail: POP settings and POP vs IMAP · Gmail: add Gmail to another email client · Microsoft: Outlook.com POP, IMAP and SMTP settings · Microsoft: POP3 and IMAP4 in Exchange Online · Microsoft: send email from apps and devices · Twilio SendGrid: SMTP ports
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What is the difference between IMAP and SMTP?
SMTP (Simple Mail Transfer Protocol) sends email: from your app to your provider, and from server to server. IMAP (Internet Message Access Protocol) reads email that has already arrived, and keeps folders and read status in sync across every device you use.
SMTP vs IMAP: do I need both?
Yes, for a normal mailbox. Your email client uses SMTP for outgoing mail and IMAP (or POP3) for incoming mail, which is why setup screens ask for an incoming and an outgoing server. An app that only sends notifications needs SMTP alone.
Is IMAP incoming or outgoing?
Incoming. IMAP retrieves and syncs mail from your mailbox. Outgoing mail always goes through SMTP. In Gmail, for example, incoming is imap.gmail.com on port 993 and outgoing is smtp.gmail.com on port 587 or 465.
POP3 vs SMTP: what's the difference?
Like IMAP, POP3 is for receiving: it downloads messages from the server to one device. SMTP is for sending. The difference between POP3 and IMAP is syncing. Google describes POP as suited to a single computer, while IMAP syncs in real time across devices.
Which SMTP port should I use?
Use 587 with STARTTLS or 465 with implicit TLS, whichever your provider supports. Microsoft 365 and Outlook.com use 587. Gmail accepts both. Port 25 is for server-to-server relay, and 2525 is not an official SMTP port, though some sending services accept it.
Should I use IMAP or POP3?
IMAP for almost everyone. It keeps mail on the server, so your phone, laptop and webmail all show the same folders and read status. POP3 only makes sense if you want mail downloaded to one computer.
Does a cold email tool use IMAP or SMTP?
Both. It sends your sequence through SMTP (or the provider's API, when you connect by OAuth) and watches the inbox through IMAP or the API so it can stop the sequence when someone replies.