SELECT ActivityId,BccAddress,CcAddress,CreatedById,CreatedDate,FromAddress,FromName,HasAttachment,Headers,HtmlBody,Id,Incoming,IsDeleted,IsExternallyVisible,LastModifiedById,LastModifiedDate,MessageDate,MessageIdentifier,ParentId,RelatedToId,ReplyToEmailMessageId,Status,Subject,SystemModstamp,TextBody,ThreadIdentifier,ToAddress,ValidatedFromAddress FROM EmailMessage
Your SOQL query would be like this.