If a user retrieves the value from a multi-select field, it will be in an array.Send Email actionon the other handis similar tonlapiSendEmailAPI which states that a valid recipient it will accept should be any of the following:

• A single emailaddress
• Multiple emailaddresses separated by comma
• Single Internal Id of anEntity (where the Entity record has a valid email address)

A value from a multi-select field will not be valid for theSend Email action. The workaround is to use aWorkflow Action Scriptinstead of the standardSend Email action. The workflow action script will process the value from the multi-select field for it to be valid for thenlapiSendEmailAPI.

SuiteScript 1.0:

functionsend_email(){var record =nlapiGetNewRecord();var ids = record.getFieldValues('XXXX');//where XXXX is the internal Id of the multi-select fieldfor(var i =0; i < ids.length; i++){var recipientEmail =nlapiLookupField('ENTITY', ids[i],'email');var sender =2;//internal id of sender/employeevar subject ='Test Email';var body ='Hello'; nlapiSendEmail(sender, recipientEmail, subject, body,null,null,{'entity': ids[i]});}}