Dear Niru.shetty
Good day.
Thank you for posting in Microsoft Community.
According to your description, we understand you want to use Word mail merge to send one email to multiple recipients. It works for single recipient but not for multiple recipients using Excel spreadsheet as Existing list.
For the situation you encountered, we understand it has affected your work, sorry for the inconvenience caused.
We did a test from our side, prepared a Excel list with recipients name and email address. When we tried mail merge in Word, it works, and if went to Outlook, we can see 3 emails sent out.



For troubleshooting, could you confirm information below?
We appreciate your understanding that sometimes the initial reply may not resolve the problem very soon. However, we can work together to narrow down the situation. Please kindly provide more information to let us work further.
1.Does the issue happen when you use a specific Word template do mail merge? If you try a different Word document, does it work?
2.You mentioned I have tried ; and then ", "(comma with a space), but none works when the mail is merged onto Outlook, could you share a screenshot of it?
And could you also share a screenshot of your Excel spreadsheet? Note: please mask all private information.
3.When select recipients, just for test, if you Type a New List and create new address list with several recipients, does it work? This way helps narrow down if the issue only happens when using Excel spreadsheet as Existing list.
4.What is the version of your Word application? Please go to File>Account, capture a screenshot of Product Information, as shown below.

Thanks your patience and understanding.
Hope you keep safe and healthy always!
Sincerely,
Tina | Microsoft Community Moderator