perf(email): optimize max line length calculation

Author: zangjiucheng

Lib/email/contentmanager.py

@@ -151,7 +151,7 @@ def embedded_body(lines): return linesep.join(lines) + linesep
     def normal_body(lines): return b'\n'.join(lines) + b'\n'
     if cte is None:
         # Use heuristics to decide on the "best" encoding.
-        if max((len(x) for x in lines), default=0) <= maxlen:
+        if max(map(len, lines), default=0) <= maxlen:
             try:
                 return '7bit', normal_body(lines).decode('ascii')
             except UnicodeDecodeError:

Misc/NEWS.d/next/Library/2025-06-10-18-02-29.gh-issue-135307.fXGrcK.rst

@@ -1,2 +1,3 @@
-:mod:`email`: Ensure policy accepts unlimited line lengths by
-treating falsey values as :data:`sys.maxsize`.
+:mod:`email`: Fix exception in set_content when encoding text
+and max_line_length is set to :const:`0` or :const:`None`
+(unlimited).