As discussed in the Mailmerge Tips & Tricks 'Sticky' thread at the top of this forum (https://www.msofficeforums.com/mail-...ps-tricks.html), under the Mailmerge Data Format Problems heading, the problem with your "middle initial" field is most likely due to that column having mixed data types. Likewise, further down the page, is the topic Mailmerge US Zip Code Formatting, where a field code to resolve your zip code issues is presented.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]