印刷用テンプレートで引用を<blockquote>に変換して、CSSで左側に線を入れると引用を線で表示して印刷できます。たとえば以下のテンプレートをprint.templateとして保存するとそれらしくなります。
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <title>{@HtmlEscape(@Subject())}</title> <style type="text/css"> body {{ margin-left: 3em; margin-right: 3em; }} .header-title {{ font-weight: bold; font-size: 90%; }} .header-value {{ font-size: 90%; }} .body {{ font-family: monospace; }} blockquote {{ border-width: 0px 0px 0px 2px; border-color: blue; border-style:solid; padding-left:1em; margin-left: 0.5em; }} </style> </head> <body> <table border="0" cellspacing="0" cellpadding="0"> <tr> <td colspan="2"><hr size="3" style="color: lightblue"></td> </tr> <tr style="padding-bottom: 5px;"> <td width="70" nowrap class="header-title">To: </td> <td width="100%" class="header-value">{@HtmlEscape(@FormatAddress(To))}</td> </tr> {@If(Cc, @Concat(' <tr style="padding-bottom: 5px;"> <td width="70" nowrap class="header-title">Cc: </td> <td width="100%" class="header-value">', @HtmlEscape(@FormatAddress(Cc)), '</td> </tr>'), '')} <tr style="padding-bottom: 5px;"> <td width="70" nowrap class="header-title">From: </td> <td width="100%" class="header-value">{@HtmlEscape(@FormatAddress(From))}</td> </tr> <tr style="padding-bottom: 5px;"> <td width="70" nowrap class="header-title">Date: </td> <td width="100%" class="header-value">{@FormatDate(@Date(Date), '%D %M1 %Y4 %h:%m:%s %z')}</td> </tr> <tr> <td width="70" nowrap class="header-title">Subject: </td> <td width="100%" class="header-value">{@HtmlEscape(@Subject())}</td> </tr> <tr> <td colspan="2"><hr size="3" style="color: lightblue"></td> </tr> <tr> <td colspan="2" class="body"><p>{-@Script(<<END function getQuoteDepth(s) { var depth = 0; var n = 0; for (n = 0; n < s.length; ++n) { var c = s.charAt(n); if (c == '>') ++depth; else if (c == ' ' || c == '\t') ; else break; } return { "index": n, "depth": depth }; } function escape(s) { return s.replace(/&/g, "&").replace(/</g, "<"); } var body = ""; var lines = arguments(0).split("\n"); var quote = 0; for (var n = 0; n < lines.length; ++n) { var line = lines[n]; var qd = getQuoteDepth(line); var q = qd.depth; if (q > quote) { for (var m = 0; m < q - quote; ++m) body += "<blockquote>"; } else if (q < quote) { for (var m = 0; m < quote - q; ++m) body += "</blockquote>"; } quote = q; body += escape(line.substring(qd.index)); body += "<br>"; } result.value = body; END , 'JScript', @Body('', :BODY-RFC822INLINE))-}</p></td> </tr> </table> </body> </html>