Local-Part

What is the Local-Part of an email address?

The local-part is the portion of an email address that appears before the “@” symbol. It uniquely identifies a mailbox or user within a specific domain. For example, in the address support@example.com, the local-part is support. Together, the local-part and the domain name form the complete address that allows mail servers to route messages correctly to their intended recipients.

The local-part can contain letters, numbers, and certain special characters, depending on the rules defined in RFC 5321. However, some characters require quotation marks or escaping to be valid. While many systems only allow simple names like info or admin, others support more complex formats for aliases, departmental routing, or automated message handling.

How the Local-Part Works

When an email is sent, the SMTP protocol uses the local-part and domain to determine the delivery path. The domain directs the message to the right mail server, while the local-part tells that server which specific mailbox or alias should receive it.

Examples of local-parts include:

• john.doe – a standard username format
• sales – a departmental address
• info – a general-purpose inbox
• support+eu – an address using a plus tag for filtering

Mail servers interpret the local-part according to their configuration. Some treat dots as separators (john.doe ≠ johndoe), while others ignore them. Many systems also support “plus addressing,” where anything following a plus sign is treated as a label for sorting or filtering (for example, support+billing@example.com).

Formatting Rules and Best Practices

Although the local-part allows a wide range of characters, using simple, predictable names is best for compatibility and deliverability. Some characters can trigger errors or be rejected by older or restrictive mail systems.

Key formatting guidelines include:

• Allowed characters: A–Z, a–z, 0–9, and special symbols like period (.), hyphen (-), and underscore (_)
• Quotation marks are required for special characters or spaces ("John Smith"@example.com)
• Local-parts are case-sensitive by standard, but most servers treat them as case-insensitive
• Keep names concise and descriptive for easier user management
• Avoid special or non-ASCII characters unless necessary

Consistent naming conventions make administration easier and prevent conflicts between aliases, forwarding rules, and departmental mailboxes.

Local-Part and DMARCeye

DMARCeye analyzes the complete address structure in authentication data to identify patterns of legitimate and unauthorized usage. While DMARC focuses primarily on domain-level identity, understanding the local-part helps trace which internal users, systems, or aliases are responsible for outgoing mail.

The platform’s reporting engine highlights local-parts involved in failed authentication attempts or spoofing attempts, giving organizations a clearer view of which accounts or aliases may be at risk. This insight helps refine policy enforcement, strengthen internal governance, and protect users from targeted impersonation or abuse.

Sign up for a free trial of DMARCeye today and secure your email domain.

To learn more about DMARC and DMARC-related terms, explore the DMARCeye Glossary.