I was experiencing some issues with email notifications, specifically when including multi-column list fields. Spaces were being inserted into the HTML, causing tags and styles to appear broken.
I did some research and found that when a single line exceeds 998 characters, it causes problems with the PHP mail function.
I fixed it by making this change to common.php, on line 1665:
$is_success = wp_mail($to, $subject, $message, $headers, $attachments);
was changed to
$is_success = wp_mail($to, $subject, wordwrap($message), $headers, $attachments);
Due to the way the email messages are assembled via string concatenation without any built in line breaks, I can only assume that other users must have encountered this issue as well. Would it be possible to add the wordwrap() into the next Gravityforms release?