private static boolean shouldEncodeQuotedPrintableOrWrap(String s, int posInLine) {
        int lineLength = posInLine;
        int length = s.length();
        for (int i = 0; i < length; i++) {
            char c = s.charAt(i);
            if (c != '=' && c != '\t' && shouldEncodeQuotedPrintable(c)) {
                return true;
            }
            if (c == '\r' || c == '\n') {
                lineLength = 0;
                continue;
            }
            if (++lineLength > HARD_LINE_LIMIT_EXCLUDING_CRLF) {
                return true;
            }
        }
        return false;
    }
https://www.rfc-editor.org/rfc/rfc5322#section-3.4
https://www.rfc-editor.org/rfc/rfc5322#section-3.6.2
turms-plugins/turms-plugin-push/src/main/java/im/turms/plugin/push/core/smtp/codec/MailEncoder.java