diff --git a/runtime/ftplugin/sieve.vim b/runtime/ftplugin/sieve.vim
index 8161fe99ac..1ea8eaeb9d 100644
--- a/runtime/ftplugin/sieve.vim
+++ b/runtime/ftplugin/sieve.vim
@@ -3,6 +3,7 @@
 " Maintainer:           This runtime file is looking for a new maintainer.
 " Previous Maintainer:  Nikolai Weibull <now@bitwi.se>
 " Latest Revision:      2025 Feb 20
+" 2026 Jan 09 by Vim Project: preserve line endings for existing files #19144
 
 if exists("b:did_ftplugin")
   finish
@@ -16,4 +17,7 @@ setlocal formatoptions-=t formatoptions+=croql
 
 " https://datatracker.ietf.org/doc/html/rfc5228#section-2.2 says
 " "newlines (CRLF, never just CR or LF)"
-setlocal fileformat=dos
+" Use CRLF for new files only; preserve existing line endings
+if expand('%:p') !=# '' && !filereadable(expand('%:p'))
+  setlocal fileformat=dos
+endif
diff --git a/scripts/vim-patch.sh b/scripts/vim-patch.sh
index f7c2d72718..5e4848f365 100755
--- a/scripts/vim-patch.sh
+++ b/scripts/vim-patch.sh
@@ -179,10 +179,10 @@ assign_commit_details() {
   local vim_coauthor0
   vim_coauthor0="$(git -C "${VIM_SOURCE_DIR}" log -1 --pretty='format:Co-authored-by: %an <%ae>' "${vim_commit}")"
   # Extract co-authors from the commit message.
-  vim_coauthors="$(echo "${vim_message}" | (grep -E '^Co-authored-by: ' || true) | (grep -Fxv "${vim_coauthor0}" || true))"
+  vim_coauthors="$(echo "${vim_message}" | (grep -E '^Co-[Aa]uthored-[Bb]y: ' || true) | (grep -Fxv "${vim_coauthor0}" || true))"
   vim_coauthors="$(echo "${vim_coauthor0}"; echo "${vim_coauthors}")"
   # Remove Co-authored-by and Signed-off-by lines from the commit message.
-  vim_message="$(echo "${vim_message}" | grep -Ev '^(Co-authored|Signed-off)-by: ')"
+  vim_message="$(echo "${vim_message}" | grep -Ev '^(Co-[Aa]uthored|Signed-[Oo]ff)-[Bb]y: ')"
   if [[ ${munge_commit_line} == "true" ]]; then
     # Remove first line of commit message.
     vim_message="$(echo "${vim_message}" | sed -Ee '1s/^patch /vim-patch:/')"