What is SMTP host name?

The SMTP host name refers to the Fully Qualified Domain Name (FQDN) of the mail server that sends and receives email using the SMTP protocol. It is used to identify the specific SMTP server handling mail transmission for a domain via DNS records and during SMTP envelope handshake process.

What is SMTP host name?

Overview of SMTP Host Name

The SMTP host name signifies the unique identity of a domain’s mail server:

  • Also known as Mail Exchanger hostname, MX hostname, destination host etc.
  • Used during SMTP envelope transmission to identity mail server.
  • Structured as subdomain+hostname+top-level domain.
  • Example – mail.example.com, smtp.example.net etc.
  • Resolved to server IP address via MX DNS records to route mail.
  • Provided during SMTP banner HELO / EHLO handshake commands.

So in summary, the SMTP host name offers recognizable moniker to identify SMTP server for mail routing purposes.

Role of SMTP Host Name in Email Delivery

The SMTP host name plays an important role facilitating email transmission as:

  • It is published in public DNS through MX records to locate mail server addresses.
  • Helps determine the target SMTP server to which messages should be delivered for a domain.
  • Provided to initiating SMTP server during envelope handshake to identify domain identity.
  • Used by receiving SMTP server during banner confirmation to verify connecting server.
  • Enables segmentation of mail handling from web or other services through subdomain.
  • Assists with diagnostics, logging, troubleshooting and tracing.

So the unique hostname allows singling out the mail server in infrastructure and DNS resolutions.

Format of SMTP Host Name

The standard format convention for SMTP host names is:


  • Subdomain (optional) – smtp, mail, mx etc. Identifies function.
  • Hostname – Server machine hostname e.g. server1.
  • Domain – Organization domain e.g. example.com.
  • TLD – Top level domain (.com/.org/.net etc).
  • FQDN – Fully qualified domain name.

Some examples are mail.example.com, smtp.example.org, mx01.example.net etc.

Subdomains like ‘mail’, ‘smtp’ and ‘mx’ are commonly used to designate mail handing server.

How SMTP Host Name is Used

The SMTP host name serves multiple usage contexts:

DNS Records

The SMTP hostname is published in MX DNS records to map identity of mail server for domain.

Routing Mail

MX records are queried to resolve SMTP hostname into IP address for routing mail to destination domains.

Envelope Handshake

Provided during initial SMTP banner greeting by sender and receiver servers for establishing conversation.

Identifying Server

Unique SMTP hostname allows administrators to identify and distinguish mail server among other systems.

Logging Transactions

Hostname helps tag and trace SMTP transactions to specific mail server instance in logs.


Used for validating server identity and implementing sender policies like SPF.

So in summary, SMTP hostnames standardize server identity across DNS, envelope, policies, logging and diagnostics.

Determining SMTP Host Name

When determining SMTP hostname to use, key considerations are:

  • Reflect server function through subdomain – smtp, mail etc.
  • Pick descriptive, unique and consistent server hostname.
  • Use organization’s existing domain. Add target domain as subdomain if handling multiple domains.
  • Follow naming conventions based on server OS – emailserver1.domain.com etc.
  • Use hostname to indicate region, number etc. if running multiple mail servers – smtp-eu.domain.com
  • Set both FQDN and short hostname on server for interoperability.

So choose easy to recognize and resolve names that identify the SMTP server deployment uniquely within the organizational context.

Setting SMTP Host Name on Mail Server

To configure SMTP hostname on the mail server:

On Windows

  • Open Control Panel > System > Computer Name.
  • Change domain and hostname and click OK. Reboot.

On Linux

  • Edit /etc/hostname file to change short hostname.
  • Edit /etc/hosts file to set FQDN mapping to IP.
  • Reboot server for settings to take effect.
  • Use hostnamectl or hostname commands if available.

So in summary, the SMTP hostname parameters can be configured directly on both Windows and Linux operating systems powering the mail server either via UI settings or text files.

Key Takeaways on SMTP Host Name

  • The SMTP host name uniquely identifies the mail server handling sending and receiving of emails.
  • It is typically structured as subdomain+hostname+domain e.g. smtp.server1.domain.com
  • SMTP hostname allows distinguishing mail server in infrastructure and DNS resolutions.
  • It is provided during SMTP envelope EHLO / HELO banner greeting and encoded in MX records.
  • Choose descriptive and identifiable SMTP hostnames reflecting server deployments.
  • Set at OS level and propagate via DNS for visibility. Use hostname conventions based on environment.


The SMTP hostname designates the identity of the mail server handling email transmission for a domain in various contexts from DNS records to envelope conversations. A standardized naming convention helps uniquely recognize SMTP servers in heterogeneous infrastructure deployments. Meaningful naming also assists with diagnostics, logging and general administration. Technically optional, adopting expressive and memorable SMTP hostnames improves manageability and organization. Therefore tuning hostname parameters on mail servers and keeping DNS records aligned pays back through operational transparency when navigating complex email architectures.


  1. Can I use IP address instead of SMTP hostname in configurations?
    It is recommended to use full SMTP hostnames instead of just IPs even if functional as it provides context and prevents breakage if IPs change.
  2. What are common SMTP subdomain prefixes used?
    Common SMTP subdomains are mail, smtp, mx, mx1 etc. But any subdomain can be used as long as corresponding MX DNS records are created for resolution.
  3. Does capitalization matter for SMTP hostnames?
    Yes, capitalization impacts resolution. Hostnames should be consistently lowercase to avoid issues. But domains can be uppercase by convention.
  4. How do I find my SMTP hostname?
    The SMTP hostname being used for sending mail can be determined by checking envelope headers of emails sent from the domain to see HOST specified.
  5. Can I use the same SMTP hostname for multiple servers?
    It is recommended to assign unique hostnames to avoid issues. If you have multiple environments, use region, number etc. to differentiate hostnames.
  6. Should punctuation be used in SMTP hostnames?
    Avoid using underscores or special punctuation within hostnames. Stick to alphanumeric phrases separated by dashes or dots only for broadest compatibility.
  7. Does changing SMTP hostname affect email delivery?
    Yes, you need to update corresponding DNS MX records if SMTP hostname is changed for seamless delivery. May take upto 48 hours to propagate through DNS caches.
  8. Why are domain and subdomain redundant in FQDN?
    Repeating domain and subdomain in FQDN eliminates ambiguity. The subdomain prefixes like smtp provide functional context to hostname.
  9. Can I use IP address in MX records?
    It is recommended to use FQDN like smtp.domain.com in MX records instead of just IP address to prevent service breakage if IP address changes in future.
  10. What is the difference between MX record and SMTP host name?
    MX record specifies FQDN of mail server. SMTP host name is the server identity configured on the machine itself handling mail corresponding to MX record.
  11. How does specifying SMTP hostname help with deliverability?
    Unique consistent SMTP hostnames allow receivers to apply filters thereby improving deliverability to valid servers and restricting suspicious sources.
  12. Can multiple domains share an SMTP hostname?
    Ideally each domain should have its own dedicated SMTP hostname. If managing multiple domains, use domain name as subdomain for isolation.
  13. Can web and mail servers share same hostname?
    It is recommended to assign separate identities using distinct subdomains like www and smtp to avoid conflicts between web and mail configurations that can break services.
  14. How long can an SMTP hostname be?
    Technically up to 253 characters but keeping hostname length below 63 characters is recommended for compatibility with older systems.
  15. Can I use an IP address or domain in SMTP banner?
    Using FQDN hostname in EHLO/HELO SMTP banner is recommended. IP or just domain without hostname can cause issues.
  16. Does changing SMTP hostname affect SPF records?
    Yes, you need to update SPF DNS records to include the new SMTP hostname identity if you have configured SPF policies for preventing email spoofing.
  17. Can I use emojis or special characters in SMTP hostname?
    No, stick to plain alphanumeric characters separated by dots and dashes only. Using emojis or special characters risks breaking DNS resolution and compatibility.
  18. How often should the SMTP hostname be changed?
    Change only if necessary for isolation purposes. Avoid frequent changes as hostname transition requires updates to DNS records, configurations etc. to avoid disruption.
  19. Does using Secure SMTP require having separate hostname?
    No, same hostname can be used for both plain and implicit TLS SMTP servers. Use different ports and security credentials to isolate them.
  20. Can I use hostname root domain in SMTP EHLO greeting?
    No, provide the full subdomain+hostname+domain instead of just root domain during EHLO as it fails DNS validation and risks deliverability flagging as spam.

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