Subscriber Email Address Validation in Marketing Cloud Engagement

Marketing Cloud Engagement detects invalid email addresses using the following two mechanisms:

1. Invalid address detection at import time

2. List Detective

1. Invalid Address Detection at Import Time

This validation runs when importing to a list (excluding All Subscribers) or a data extension with an EmailAddress-type field. The system checks email address syntax and returns an "Invalid email address" error when a problem is detected.

Note: Results may vary depending on the import method.

Examples of addresses flagged as invalid:

• Contains two or more @ symbols (e.g., abcd@@example.com)

• Top-level domain is one character or does not exist (e.g., mailto:abcd@example.c, abcd@example)

• Contains multibyte characters (e.g., あいうえお@example.com)

• Contains spaces within the address (e.g., abcd@ example.com, abcd @example.com)

• Does not contain @ (e.g., abcdexample.com)

Examples of addresses NOT flagged as invalid:

• Period immediately before @ (e.g., mailto:abcd.@example.com)

• Consecutive multiple periods (e.g., ab….cd@example.com)

In addition, the EmailAddress-type field in a data extension has the following limits: the local part (before @) can be up to 100 characters, and the total email address length (including domain) can be up to 254 characters.

2. List Detective

The detailed conditions used by List Detective are not disclosed, as they are maintained to protect deliverability across the service. However, role-based local parts such as admin@ and info@, and common misspellings of well-known domains, are examples of addresses flagged as List Detective violations.

Note: These conditions are subject to change.

List Detective operates at the following two points:

• At import time (excluding data extensions)

• At send time

For email addresses that cannot be sent due to List Detective, enable Custom List Detective and submit an exception request to support to allow sending to those addresses.

Important:

• Custom List Detective can only be configured at the enterprise level, so it is automatically inherited by all business units associated with the account or organization, including any newly created business units.

• Custom List Detective is intended to maintain and improve the quality of your send list for deliverability and security purposes. Exception requests for clearly incorrect addresses (e.g., misspellings of well-known domains such as gmai.com) may not be accepted. In such cases, list cleansing is strongly recommended.

Subscribers excluded from a send job due to "List Detective" can be identified in the Not Sent Report available through the Tracking Extract in the Data Extract Activity.

Note that a successful import to a data extension does not guarantee that the email can be sent.

FAQ

Q: An email address imported to a data extension without issues is not being sent. Why?

A: Although the EmailAddress-type field in a data extension may accept the import without error, sending may still fail. This can occur when a subscriber is not registered in All Subscribers at send time — the system creates a record in All Subscribers and writes the data extension email address to the Email Address field on that record, which may then trigger a List Detective violation. Subscribers excluded for this reason can be confirmed in the Not Sent Report from the Tracking Extract.

Being importable into a data extension does not necessarily mean the email can be sent.

Q: Does Marketing Cloud's email address validation follow RFC 5322? Will non-compliant addresses result in import errors?

A: No. Some RFC non-compliant addresses are intentionally allowed to be sent, as they are known to be in actual use. The validation logic for determining "invalid email addresses" is complex and cannot be expressed with a simple regular expression. For the basic validation rules, refer to the following documentation: