Which statement is not a rule for the data source for the mail merge?

the top line must contain the names of the fields being using in the merge.
each field name in the data source must be unique.
field names can be any size.
field names should start with a letter.

Field names should start with a letter  is not a rule for data source for a mail merge.

Explanation:

The best Microsoft tool to use for a data source in a Microsoft mail merge is Excel spreadsheet, a data source for a mail merge can also be a database or a table .

Mail merge is the merging/combining of mail and letters or labels meant for mailing in mass from a form letter. this simply means that Microsoft word documents can take in content from databases, spreadsheet.

A data source is used to define the connection between a data from its source to its recipient. it is the name used when querying a data .

every other options given is a rule because it makes the field name unique and easy to query the data source as well