What is a dotted hostname in the context of email and DNS records?

Key findings

• Terminology Confusion: The phrase "dotted hostname" is not a standard term in email or DNS, leading to ambiguity and a need for further clarification from the party using it.
• RFC Compliance: A client referring to a "dotted hostname" as not being a "real" domain (with SOA records) suggests a misunderstanding of how DNS zones and delegation work. A proper domain for email sending typically requires a fully managed DNS zone.
• Hostnames vs. Domain Names: In DNS, all names are technically domain names or labels, and the distinction between a hostname and a domain name (as understood by the client) often comes down to whether it hosts services or represents a delegated zone.
• Email Usage: While a hostname (e.g., a subdomain like mail.example.com) can technically be used in both 5321.MailFrom and 5322.From addresses, using it for general marketing or transactional emails is not recommended due to potential deliverability issues.
• Domain Delegation: Ultimately, the client's concern likely revolves around domain delegation (or lack thereof) rather than a unique type of hostname, implying a setup where a subdomain might be managed differently from the root domain.

Key considerations

• Clarify Terminology: Always seek clarification when encountering non-standard terms. Understanding the client's specific setup and concerns is paramount to providing accurate guidance.
• RFC Compliance for Deliverability: Adhering to RFC standards for DNS and email, including having proper SPF, DKIM, and DMARC records, is crucial for modern email deliverability and avoiding blocklists.
• Subdomain Strategy: If a client is hesitant about using a full domain, transitioning a "dotted hostname" into a properly configured subdomain (e.g., marketing.example.com) is a common and effective approach for email sending, allowing for dedicated reputation management.
• Purpose of Email: For critical emails (e.g., marketing, transactional), always recommend using a fully qualified domain or subdomain with a complete DNS setup, including SOA records where appropriate.

Key opinions

• Uncommon Terminology: Many marketers find "dotted hostname" to be an unusual term, indicating it's not part of common industry parlance for email or DNS.
• Context is Key: Without specific context from the client, understanding what they mean by such a term is nearly impossible, making effective problem-solving difficult.
• RFC Non-Compliance Risks: If a client is aware their setup isn't RFC compliant, it signals potential deliverability challenges that marketers must address, especially concerning email authentication.
• From Address Best Practices: Using an unconventional or poorly configured hostname for the email From address (5322.From) is generally advised against for marketing or transactional mail, favoring dedicated domains or subdomains.

Key considerations

• Direct Client Communication: When faced with ambiguous terminology, the most effective approach is to directly ask the client for clarification on their specific setup and intentions.
• Subdomain Conversion: If a client is using a "dotted hostname" for a particular reason, converting it into a standard subdomain for email purposes can be achieved without disrupting existing services, while also improving email deliverability. This often involves ensuring proper DNS record configuration.
• Focus on Deliverability: Regardless of terminology, the ultimate goal is ensuring emails reach the inbox. This means verifying correct DNS records, email authentication, and reputation management. Proper MX records and other setup are critical.
• Manage Client Expectations: Educate clients on the importance of standard domain and DNS configurations for reliable email sending, setting realistic expectations if their current setup is unconventional.

Key opinions

• No Technical Distinction: Within DNS, there is no literal distinction between a hostname and a domain name; they are all referred to as domain names or labels.
• Hostname Definition: A hostname typically refers to a name with an A record but no NS records or SOA record, regardless of how many dots (subdomains) are present in its FQDN.
• Validity for Email: A hostname is technically valid for both 5321.MailFrom and 5322.From addresses.
• Recommended Use: Experts advise against using a bare hostname for the 5322.From address for anything beyond system messages, due to potential deliverability challenges.
• Delegation Misconception: The client's use of "dotted hostname" likely refers to a lack of proper domain delegation (i.e., not a separate zone with its own SOA).

Key considerations

• DNS Record Requirements: Regardless of whether a name is called a "hostname" or a "domain name," it must have appropriate MX, SPF, and potentially DKIM records to send email reliably.
• Subdomain Conversion: If a client is determined to use a specific hostname, it can often be effectively managed as a subdomain, ensuring proper DNS hierarchy and email deliverability without harming existing configurations.
• Clarify Client Intent: It's critical to ascertain what the sender truly means by their non-standard terminology to diagnose and resolve the underlying issue effectively. Often, this reveals a misunderstanding of core DNS concepts.
• Avoiding IP in Hostname: Be wary if a client implies an IP address within the hostname, as this is not a standard or advisable practice for email sending domains.

Key findings

• DNS Hierarchy: DNS names are hierarchical, with dots separating labels that indicate different levels of a domain or specific hostnames within that domain.
• Fully Qualified Domain Names (FQDN): Any complete domain name that specifies its position in the DNS hierarchy, typically ending with a root dot (though often omitted), is an FQDN, and can function as a hostname.
• SOA Records: A key distinction of a "real" domain or zone is the presence of an SOA (Start of Authority) record, which signifies where definitive information about that zone can be found. A hostname without an SOA is managed under its parent domain's SOA.
• Email Protocols and Hostnames: Email RFCs (like RFC 5321 for SMTP and RFC 5322 for message format) primarily refer to domain names in email addresses, which can be hostnames.

Key considerations

• Full Delegation for Control: For full control over a domain's DNS records (including MX, SPF, DKIM, and DMARC), it should be a fully delegated zone with its own SOA record. This ensures independence from a parent domain's policies or management.
• Impact of Trailing Dots: Some DNS configurations may treat a trailing dot differently. A trailing dot signifies a fully qualified (absolute) name, preventing relative path resolution.
• DNS Record Management: Regardless of terminology, ensuring correct DNS record types (e.g., A, MX, TXT for SPF and DMARC) are published is essential for email authentication and deliverability.
• Distinguishing Hostname Use: RFCs typically specify that email addresses use domain names. A hostname within a larger domain can certainly be a valid part of an email address, but its specific DNS setup for email must be correct.