By default, mailmerges suppress blank lines. Is that not happening for you? Is each line terminated by a paragraph break?
Have you tried the
Mailmerge Empty Space Suppression &
Mailmerge Empty Line Suppression methods described in the
Mailmerge Tips and Tricks 'Sticky' thread at the top of this forum?:
https://www.msofficeforums.com/mail-...ps-tricks.html