For more info, see Mail merge: Edit recipients. With Outlook as the mail client it works as long as the letter is in English. Now the letter should be merged into email messages. I click the 'Merge to email' button, addresses taken from the Excel sheet.
For more info, see Data sources you can use for a mail merge. I write a letter in Word, using mail merge with the name as a field in the greeting line.
To change addresses in mail merge document Open the mail merge document and choose Edit Recipient List to sort, filter, and choose specific addresses. For more information, see Prepare your Excel data source for mail merge in Word.