To find out what SMTP server is being used, you need to check the outgoing mail server settings in your email client or examine the email message headers. The SMTP server is typically listed as the “Outgoing Mail Server (SMTP)” in account settings, and in email headers, it appears in the “Received” lines showing the sending mail server. By reviewing these areas, you can quickly identify the SMTP server responsible for sending emails.
Now let’s explore this in detail — whether you’re troubleshooting email issues, auditing a mail system, configuring a website, or verifying email authentication.
What Is an SMTP Server?
SMTP (Simple Mail Transfer Protocol) is the technology responsible for sending email messages across the internet. Whenever you send an email, your device connects to an SMTP server, which then transfers the message to the recipient’s mail server.
Common examples include:
- Gmail → smtp.gmail.com
- Outlook → smtp.office365.com
- Hosting providers → mail.yourdomain.com
For example, if you’re using Gmail, your outgoing server is usually smtp.gmail.com. If you’re using Microsoft Outlook with Microsoft 365, the SMTP server is typically smtp.office365.com.
How to Find Out What SMTP Server Is Being Used? Step-by-Step Guide
Method 1: Check SMTP Server in Email Client Settings
This is the easiest method.
In Outlook
Steps:
- Open Outlook.
- Run to File > Account Settings > Account Settings.
- Select your email account.
- Click Change.
- Look at the Outgoing mail server (SMTP) field.
There you’ll see the SMTP server being used.
In Thunderbird
Steps:
- Open Thunderbird.
- Click Account Settings.
- Scroll down to Outgoing Server (SMTP).
- Check the Server Name column.
This shows which SMTP server your account is using.
On Mobile Devices
On Android or iPhone:
- Open Mail settings.
- Tap your email account.
- Look under Outgoing Mail Server.
- The SMTP address will be listed.
Method 2: Check the Email Header (Most Accurate Way)
If you received an email and want to know which SMTP server sent it, checking the message header is the most reliable method.
Every email includes hidden technical information called email headers. These show the path the email took across mail servers.
How to View Email Headers in Gmail
Steps:
- Open the email.
- Click the three dots (⋮).
- Select Show original.
- Look for lines starting with:
Received: from
The first “Received” line often shows the SMTP server used to send the message.
What to Look for in Headers
Example:
Received: from smtp.gmail.com (mail-oi1-f169.google.com)
This tells you the sending SMTP server was Gmail’s.
Another example:
Received: from mail.yourdomain.com
That indicates a hosting provider’s SMTP server.
Method 3: Check Website SMTP Configuration (WordPress or Apps)
If you’re trying to find the SMTP server used by a website:
In WordPress
- Log in to the dashboard.
- Run to your SMTP plugin (e.g., WP Mail SMTP).
- Check the SMTP Host field.
It may show:
- smtp.gmail.com
- smtp.office365.com
- mail.yourdomain.com
- A third-party provider like SendGrid
Developers often configure custom SMTP services instead of default hosting mail servers for better deliverability.
Method 4: Use Command Line (Advanced Users)
You can test SMTP connections using Telnet:
telnet smtp.gmail.com 587
If it connects, that server is reachable and likely being used.
This method is useful for:
- Network troubleshooting
- Firewall testing
- Server audits
Common SMTP Server Types
Public Email Providers
- Gmail → smtp.gmail.com
- Outlook → smtp.office365.com
- Yahoo → smtp.mail.yahoo.com
Hosting Company SMTP
Often formatted as:
- mail.yourdomain.com
- server123.hostingcompany.com
Dedicated SMTP Services
Businesses often use:
- SendGrid
- Mailgun
- Amazon SES
These are used for bulk and transactional emails.
Why It’s Important to Know Your SMTP Server
Understanding your SMTP server helps with:
- Fixing “email not sending” errors
- Resolving authentication failures
- Setting correct ports (465 or 587)
- Improving email deliverability
- Configuring SPF, DKIM, and DMARC
- Avoiding spam folder issues
If emails are bouncing or going to spam, checking the SMTP server is the first troubleshooting step.
How to Identify SMTP Server by Domain
If you don’t have access to the email client:
- Look at the email address domain (e.g., @company.com).
- Check DNS MX records using tools like MXToolbox.
- At times, the SMTP server same the mail server domain.
However, MX records show receiving servers, not always the sending SMTP server — so checking headers is more accurate.
SMTP Port Numbers to Verify
When identifying the SMTP server, also check:
- Port 587 (TLS) – Recommended
- Port 465 (SSL)
- Port 25 (Older, often blocked)
Correct port + correct server = working outgoing mail.
Common Problems When Identifying SMTP Servers
Problem 1: Multiple “Received” Lines
Emails pass through many servers. Focus on the earliest sending server.
Problem 2: Using Webmail
If you send from webmail, the SMTP server may not be visible in settings — use headers instead.
Problem 3: Cloud Email Routing
Some services use relays, so the visible SMTP server may differ from the primary provider.
Security Considerations
Never publicly share:
- SMTP username
- SMTP password
- Authentication credentials
If you discover unknown SMTP servers in headers, your account may be compromised.
Best practice:
- Enable 2FA
- Use app passwords
- Monitor login activity
- Regularly audit email headers
Quick Checklist to Find SMTP Server
- Check the email client’s outgoing settings
- View full email headers
- Inspect the WordPress SMTP plugin
- Use command-line testing
- Confirm the correct port and encryption
- Verify the authentication method
Final Thoughts
Finding out what SMTP server is being used is straightforward if you know where to look. The most direct methods are checking your email client’s outgoing server settings or examining the email headers for the sending server details.
Whether you’re troubleshooting delivery issues, configuring a website, or auditing your email system, identifying the SMTP server is a critical first step. Once you know the server, you can verify ports, encryption, authentication, and improve your overall email reliability.
Understanding your SMTP setup gives you full control over email performance, security, and deliverability — which is essential for both personal users and businesses alike.
