The "Argument was not a valid email" error occurs when a mailing fails because one or more email addresses in your contact data do not meet Acoustic Campaign's email format and validation requirements.

What causes this error

Acoustic Campaign validates email addresses before sending a mailing. If any record contains an invalid value in the Email field, the send may fail. Common examples of invalid email values include:

• Blank or empty email fields
• Missing or incorrect email format (for example, missing @ or domain name)
• Extra spaces or special characters in the email field
• Text that does not follow standard email syntax (for example, user.domain.com)
• Corrupted or incomplete data from imports or integrations

How to fix it

Step 1: Run data validation

1. Navigate to your Contact Database or Contact Source.
2. Use the built-in data validation feature.
3. Run validation to scan for email-related data issues and generate a validation report.

Step 2: Review the validation results

1. Download the validation report (CSV format).
2. Identify records flagged with invalid email values.
3. Look for patterns such as formatting issues, missing fields, or errors introduced by a recent import.

Step 3: Clean your data

Based on the validation results:

• Correct improperly formatted email addresses
• Remove or update blank email fields
• Fix malformed entries to follow standard email format
• For large datasets, consider using automated data-cleaning tools or coordinating with your data or CRM team

Step 4: Retry the mailing

1. Save and publish your updates.
2. Retry the mailing.
3. The send should proceed without the validation error.

Large databases with a small percentage of invalid records

If your database contains millions of records and only a small number are invalid:

• Focus on recently imported or updated records that may have introduced errors
• Isolate the affected contact source or segment before running validation on the full database
• Contact Acoustic Support for assistance with large-scale data validation
• Work with your data governance or IT team to prevent invalid data at the source

How to prevent this error

• Run contact data validation regularly and before large or critical mailings
• Enforce email format validation in your CRM or upstream systems
• Monitor imports and integrations for data integrity issues