How to find SMTP server?

There are a few easy methods to identify and find the SMTP server used for sending and receiving emails for an email account or domain. By checking mailbox settings, tracing email headers, looking up DNS records and using connection verification tools, the active SMTP servers powering email services can be determined.

How to find SMTP server?

Overview of Finding SMTP Servers

Some common techniques used to find the backend SMTP server handling email delivery include:

  • Checking mailbox settings or account preferences for SMTP details.
  • Examining full email headers of sent emails to identify originating host server.
  • Performing DNS lookups to fetch MX records which reveal SMTP server hostname.
  • Using Telnet or online tools to manually verify active SMTP connections.
  • Monitoring network traffic to trace SMTP conversations terminating at server IP.
  • Port scanning IPs to detect SMTP server listening on standard ports.
  • Terminal commands like ‘nslookup’, ‘dig’ to directly query DNS for MX records.

So both client-side settings and public DNS data help uncover configured SMTP mail servers.

Check Email Client Settings

One method is to check existing email client or webmail settings:

  • Webmail – Check account settings for outgoing SMTP server details.
  • Desktop clients – Inspector the preferences, connection settings for the SMTP server configured.
  • Mobile apps – View the server settings specified under account preferences.
  • Some clients auto-detect while others need manual configuration.
  • Common parameters are server name/IP, port number, SSL/TLS options.

So the mail client software storing the SMTP parameters locally often provides the configured server identity and properties.

Examine Email Headers

Another approach is examining email headers after sending a test message:

  • The full headers contain details of the mail routing and delivery.
  • Originating SMTP server name/IP is usually listed against header fields like ‘Received From’, ‘Return-Path’.
  • Other diagnostic data like destination IPs, transit times etc. also viewable.
  • Can compare headers from emails sent earlier to identify any changes in SMTP host.

So inspecting full email headers instead of brief default view exposes the underlying SMTP host coordinating the mail transmission.

Check DNS MX Records

A definitive way is checking DNS MX records for domain:

  • MX (Mail Exchange) records map domain identities to SMTP server hostnames.
  • Publicly viewable on DNS listing sites or through ‘nslookup’, ‘dig’ etc.
  • Priority points to primary SMTP server for the domain.
  • Provides full hostname like instead of just IP.

So published MX records indicate the designated mail server authoritative for sending emails from the domain.

Verify with Telnet or SMTP Tool

Another approach is checking active SMTP connections:

  • Use Telnet on ports 25 or 465 to test manual SMTP handshakes.
  • Online SMTP debugging tools also automate server verification steps.
  • Error banners reveal active server name rejecting unauthorized connection.
  • Port scans help detect listening SMTP daemons.

So basic connection tests can help confirm working configuration in addition to passive methods.

Monitor Network Traffic

For network-level visibility:

  • Inspect packet capture or mirror SMTP port connections.
  • Trace TCP sessions terminating at destination IP and port 25 to identify mail server.
  • Review firewall and security device logs showing permitted SMTP flows.

So examining network-layer data provides insight into active SMTP communication endpoints across infrastructure.

Key Things to Note

When finding SMTP servers:

  • Multiple mail servers may be deployed for redundancy evident from prioritized MX records.
  • Hostname gives better context than just IP which can map to multiple systems.
  • Server identity should ideally match MX records for reputation. But not mandatory.
  • Generic names like make differentiating SMTP systems complex on large networks.
  • DNS lookups reveal publicly visible SMTP server only which can differ from internal routing.

So check both internal configurations and public DNS data for complete context when identifying mail servers within on-premises and cloud email environments.

Finding SMTP Server of Email Services

For common email providers:

  • Gmail –
  • Yahoo –
  • –
  • Zoho Mail –
  • Protonmail –
  • Fastmail –

So the major services document or openly share their systems for integration into local clients and apps.

Key Takeaways on Finding SMTP Servers

  • Checking mailbox settings reveals the SMTP server configured locally to send mails.
  • Email headers contain trace of originating SMTP server identity and routing path.
  • Public DNS MX records map domain identities to authorized SMTP systems.
  • Manual SMTP connection tests help actively validate and confirm working configurations.
  • Monitor network traffic between SMTP client and server for flow-level visibility.
  • Combine methods for holistic context of internal and public-facing SMTP environments.


Identifying the SMTP servers handling email transmission is useful for gaining visibility into configured mail routing and diagnosing delivery issues. While domain MX records uncover public-facing systems, mailbox settings reveal internal servers actually employed. Email headers provide operational insight into transit and origin. Where possible, combining active connection verification with passive observation from multiple vantage points assembles a clear picture of the SMTP infrastructure bridging end users and recipients through reliable message transport. Determining the responsible SMTP hosts thereby allows proactively managing changes, security and performance.


  1. Where are SMTP settings located in Gmail?
    For Gmail, go to Settings > See all settings > Accounts and Import > Send mail as to view configured SMTP server details for sending emails through clients.
  2. How to check SMTP server in Outlook?
    In Outlook desktop client, go to File > Account Settings > Account Settings > Select email account > More Settings > Outgoing Server to see configured SMTP details.
  3. Can I find SMTP server used by a domain?
    Yes, querying public DNS for MX records of a domain reveals the designated SMTP systems configured to send emails from that domain.
  4. Where is SMTP server information located in email headers?
    The ‘Received From’ and ‘Return-Path’ headers typically contain the SMTP server identity in email headers which can be viewed by inspecting raw source.
  5. How can I confirm SMTP server from the command line?
    On Linux/Unix, ‘dig’, ‘nslookup’, ‘host’ commands can be used to query DNS for MX records revealing SMTP server. On Windows ‘nslookup’ can be used.
  6. Can I tell if SMTP connection is encrypted?
    Yes, when you view email headers, a section named ‘Secure Connection’ indicates if the SMTP session was protected using TLS encryption while routing the email.
  7. Can there be multiple SMTP servers for a domain?
    Yes, having multiple MX records pointing to different SMTP servers allows redundancy and failover capability in case primary SMTP server becomes unavailable.
  8. Can I find old SMTP servers used from email history?
    Yes, you can selectively compare headers from current and old emails in your mailbox to identify changes to originating SMTP server over time.
  9. What are possible SMTP server port numbers?
    Standard ports are 25 for SMTP, 465 and 587 for TLS-encrypted SMTP. But other high number ports may be used in some implementations.
  10. What does SMTP server IP in headers mean? as SMTP server IP likely indicates debugging headers added. But if persistently showing, it could mean improperly configured SMTP server identity.
  11. Where will firewall logs show SMTP traffic?
    Firewall policies allowing outbound SMTP may log permitted traffic under internet browsing or email client categories pointing to destination server IPs/ports.
  12. Can SMTP servers be identified from email envelope?
    No, envelope transmitting SMTP servers stay hidden. Only email content headers originating from submitter contain originating SMTP server identity.
  13. How can I sniff SMTP traffic to identify server?
    On local network, enable port mirroring on switch for SMTP port 25 to sniff traffic and trace TCP sessions back to originating server IP using packet capture tools.
  14. Can I identify SMTP server without sending email?
    Yes, you can find SMTP server just by checking configured client settings or DNS MX records without needing to actually send message and inspect headers.
  15. What does it indicate if DNS has no MX records for a domain?
    Lack of MX records likely indicates domain does not support email capability currently as no SMTP server is designated. Placeholder A record may exist.
  16. Can reverse DNS help identify SMTP server?
    Yes, performing a reverse DNS lookup on connecting IP can resolve to SMTP server hostname and provide additional context compared to just having IP.
  17. What if email headers show multiple Received From sections?
    Multiple received from entries indicate relaying between multiple SMTP servers across different domains. First entry is origin server while latter ones are relays.
  18. How can I automate SMTP server identification?
    Tools like nmap, Metasploit etc. allow automating port scanning, banner grabs and connection tests to detect live SMTP daemons programmatically.
  19. Is it bad if SMTP server cannot be identified?
    If SMTP server is unidentified, it likely indicates issues with network connectivity, traffic blocking, DNS failures etc. hampering mail delivery.
  20. Can end users trace intermediate SMTP relays?
    No, full routing email headers revealing intermediate hops are only included in message source for administrators. End users can only see originating server.

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