You don't need a loop to do what you were trying to do. This would do the trick

DECLARE @emails varchar(5000)=''

SELECT @emails=@emails+';'+cEmail

FROM dbo.people;

This technique, however, can give you data issues... The prefered method would be to use FOR XML PATH as discussed in the link Louis provided....

SELECT x FROM

(SELECT cEmail + ';'

FROM #people

FOR XML PATH('')) xx(x)