Bad Mail Address Error in Mail Merge

Hi

I am using Mail merge to send mails. Each cell of Excel sheet consist of 25mail IDs seperated by Commas.When I use this excel sheet “I am getting error Record Consistof Bad Mail Address”.I have tried all the combination semicolon,space and comma, still error persists
However if the cell consist of only one record it works fine.
As my Mail Size is large and hence I want to club 25 Email Ids in one mail
Please help.