We Keep Coding

how modify message body - Mimekit Message

i'm using mimekit for receive and send mail for my project. I'm sending received mails with some modifications (to & from parts). And now i need to modify in body section. I'll replace specific word with asterix chars. Specific text different for every mail. Mail may be any format. You can see i found what i want but i don't know how can i replace without any error?

MimeMessage.Body is a tree structure, like MIME, so you'll have to navigate to the MimePart that contains the content that you want to modify.
In this case, since you want to modify a text/* MimePart, it will actually be a subclass of MimePart called TextPart which is what has the .Text property (which is writable).
I've written documentation on how to traverse the MIME structure of a message to find the part that you are looking for here: http://www.mimekit.org/docs/html/WorkingWithMessages.htm
A very simple solution might be:
var part = message.BodyParts.OfType<TextPart> ().FirstOrDefault ();
part.Text = part.Text.Replace ("x", "y");
But keep in mind that that logic assumes that the first text/* part you find is the one you are looking for.

Is XSS possible through the MailAddress class?

Considering I parse user input, which is supposed to be an email address, into the MailAdress class:
var mailString = Request.QueryString["mail"];
var mail = new MailAddress(mailString);
Is there any possibility left for a cross-site-scripting attack if I output the MailAddress object later in any way? For example through a Literal control in WebForms:
litMessage.Text = "Your mail address is " + mail.Address;
Is it necessary to sanitize the outpout even though I made sure that the address is a valid email address by parsing the string?
From what I could gather the RFC for mail addresses is pretty complicated, so I am unsure if cross site scripts can be hidden in a mail address considered valid by .NET.
EDIT:
MSDN says that > and < brackets are allowed in an email address:
The address parameter can contain a display name and the associated e-mail address if you enclose the address in angle brackets. For example: "Tom Smith <tsmith#contoso.com>"
So the question remains if this is enough for an XSS attack and/or if the MailMessage class does anything to escape dangerous parts.

Generally speaking, you shouldn't need to validate the output later. However, I always recommend that you do so for the following reasons:
There may be a hole somewhere in your app that doesn't validate the input properly. This could be discovered by an attacker and used for XSS. This is especially possible when many different devs are working on the app.
There may be old data in the database that was stored before implementing/updating your filter on the input. This could contain malicious code that could be used for XSS.
Attackers are very clever and can usually figure out a way to beat a filter. Microsoft puts a lot of attention on preventing this, but it's never going to perfect. It makes the attackers job that much harder if they face and outgoing filter as well and as incoming filter.
I know it's a pain to constantly filter, but there is a lot of value in doing so. A Defense-in-Depth strategy is necessary in today's world.
Edit:
Sorry I didn't really answer the second part of your question. Based on the documentation I don't get the impression that the API is focused on sanitizing as much as it is on verifying valid formatting. Therefore I don't know that it is safe to rely on it for security purposes.
However, writing your own sanitizer isn't terribly hard, and you can update it immediately if you find flaws. First run the address through a good RegEx filter (see: Regex Email validation), then recursively remove every nonvalid character in an email address (these shouldn't get through at this point but do this for comprehensiveness and in case you want to reuse the class elsewhere), then escape every character with HTML meaning. I emphasize the recursive application of the filter because attackers can take advantage of a non-recursive filter with stuff like this:
<scr<script>ipt>
Notice that a nonrecursive filter would remove the middle occurence of <script> and leave the outer occurrence in tact.

Is it necessary to sanitize the outpout
You don't 'sanitise' output, you encode it. Every string that you output into an HTML document needs to be HTML-encoded, so if there was a < character in the mail address it wouldn't matter - you'd get < in the HTML source as a result and that would display correctly as a literal < on the page.
Many ASP.NET controls automatically take care of HTML-escaping for you, but Literal does not by default because it can be used to show markup. But if you set the Mode property of the Literal control to Encode then setting the Text like you're doing is perfectly fine.
You should make sure you always use safe HTML-encoded output every time you put content into an HTML page, regardless of whether you think the values you're using will ever be able to include a < character. This is a separation-of-concerns issue: HTML output code knows all about HTML formatting, but it shouldn't know anything about what characters are OK in an e-mail address or other application field.
Leaving out an escape because you think the value is 'safe' introduces an implicit and fragile coupling between the output stage and the input stage, making it difficult to verify that the code is safe and easy to make it unsafe when you make changes.

Matching a URL Encoded e-mail address in C#

I did some searching and didn't quite figure out why my solution is not working. Basically I need to take a string (which is HTML code) parse it and look for mailto links (which I then want to replace as part of an obfuscation). Here is what I have thus far:
string text = "<p>Some Person<br /> Person's Position<br />p. 123-456-7890<br /> e. <a title=\"Email Some Person\" target=\"_blank\" href=\"mailto:someperson%40domain.com\">someperson#domain.com</a></p>";
text = Server.UrlDecode(text);
string safeEmails = Regex.Replace(text, "()(.*?)()", "<a class=\"mailme\" href=\"$2*$4\">$6</a>");
Response.Write( Server.HtmlDecode(safeEmails));
The text is coming out of a WYSIWYG text editor (Telrik RadEditor for those familiar) and for all intents and purposes I don't have access to be able to control what is coming out of it.
Basically I need to find and replace any:
someone#domain.com
With:
<a class="mailme" href="someone#domain.com">someone#domain.com</a>
Some background: I am attempting to create a mailto link that will avoid detection by harvesters. The problem is that I receive a string with the e-mail as a standard mailto link. I cannot control the incoming string, so the mailto will always be an unprotected mailto. My object is to find all of them, obfuscate them, then use JavaScript to "fix" the link so that human vistors can easily use the mailto links. I am open to new approaches as well as modifications to the above code.

You could use a regex or the HTML agility pack to find and obfuscate all your mailto. If you want a good obfuscation try reading ten methods to obfuscate e-mail addresses compared
EDIT:
sorry, from the first version of your question I didn't get you had a problem in making your regex work. Since you're usign a WYSIWYG text editor, I think the HTML that comes out of it should be pretty "regular", so you may be fine using a regex.
You can try changing your Replace line like this:
string safeEmails = Regex.Replace(text, "href=\"mailto:.*\">(.*)</a>", "class=\"mailme\" href=\"$1\">$1</a>");

Safely insert line breaks into HTML

I have an application allows a user to copy paste html into a form. This html gets sent as an email, and the email server will not allow more than 1000 characters per line. So, I'd like to insert line breaks (\r\n) into the html after the user has hit submit. How can I do this without changing the content?
My idea is this:
html.replace('<', '\r\n<');
But is that guaranteed to not change the result? Is '<' not allowed in attributes?
Edit: I'm actually thinking this will not work because the html could have a script block with something like if(x < 3). I guess what I need is an html pretty printer that works in either js or C#.

If you Base64 encode the content, then you can break up the content into however many lines you want.

Email MIME standard uses transfer encoding techniques to solve this problem. Ideally you would be using a mail library that takes care of this for you, so you can insert lines of any length.
Using the System.Net.Mail.MailMessage class in C#, you should be able to construct a normal message and it will transfer-encode it for you. If that doesn't work, you can also construct a multi-part message with a single System.Net.Mail.AlternativeView and set the transfer-encoding explicitly.
Here is a sample I am currently using (note it has a character encoding bug, so your body text must be a unicode string):
private void Send(string body, bool isHtml, string subject, string recipientAddress, string recipientName, string fromAddress)
{
using (var message = new MailMessage(new MailAddress(fromAddress),
new MailAddress(recipientAddress, recipientName)))
{
message.Subject = subject;
var alternateView = AlternateView.CreateAlternateViewFromString(body, message.BodyEncoding,
isHtml ? "text/html" : "text/plain");
alternateView.TransferEncoding = TransferEncoding.QuotedPrintable;
message.AlternateViews.Add(alternateView);
var client = new SmtpClient();
client.Send(message);
}
}

You're getting into dangerous territory attempting to parse HTML with a replace function. The easiest method would be to just display a warning box on the form that tells the user that lines cannot be longer than 1000 characters, and return an error message if they attempt to submit content with lines over that length.
Otherwise, you could insert a linebreak after X number of characters, and insert some special markup (like <!--AUTO-LINEBREAK-->, or similar) that informs whoever is receiving the e-mail that an automatic line break was inserted.

Add normal line breaks where you think they should be. For example:
Off the top of my head, find all <p>, <table>, <tr>,<td>,<br>, and <div> tags and add a \r\n right before them.
Once that is done, loop through all the lines one more time. If there are any that are still 1000+ characters long, I would insert a \r\n in the whitespace.
Also, you should be removing any script tags from the HTML email body. Having script tags can cause all types of problems (marked as spam, marked as a virus, blocked, etc..).

I am not sure how you are delivering your email... if it is handed off to a php script that then send it to a mail server or uses the mail() method, then this link might help.
http://php.net/manual/en/function.wordwrap.php
If not, can you clarify your question a bit?
Another simply thought, is that you could use:
html.replace('','\r\n');
or:
html.replace('',''+String.fromCharCode(13));//inserts a carriage return
However, since the will ideally be parsed in the browser, inserting "\r\n" may not be effective and may actually just display as "\r\n"....
Hope any of this is helpful.

Is it possible to programmatically 'clean' emails?

Does anyone have any suggestions as to how I can clean the body of incoming emails? I want to strip out disclaimers, images and maybe any previous email text that may be also be present so that I am left with just the body text content. My guess is it isn't going to be possible in any reliable way, but has anyone tried it? Are there any libraries geared towards this sort of thing?

In email, there is couple of agreed markings that mean something you wish to strip. You can look for these lines using regular expressions. I doubt you can't really well "sanitize" your emails, but some things you can look for:
Line starting with "> " (greater than then whitespace) marks a quote
Line with "-- " (two hyphens then whitespace then linefeed) marks the beginning of a signature, see Signature block on Wikipedia
Multipart messages, boundaries start with --, beyond that you need to do some searching to separate the message body parts from unwanted parts (like base64 images)
As for an actual C# implementation, I leave that for you or other SOers.

A few obvious things to look at:
if the mail is anything but pure plain text, the message will be multi-part mime. Any part whose type is "image/*" (image/jpeg, etc), can probably be dropped. In all likelyhood any part whose type is not "text/*" can go.
A HTML message will probably have a part of type "multipart/alternative" (I think), and will have 2 parts, one "text/plain" and one "text/html". The two parts should be just about equivalent, so you can drop the HTML part. If the only part present is the HTML bit, you may have to do a HTML to plain text conversion.
The usual format for quoted text is to precede the text by a ">" character. You should be able to drop these lines, unless the line starts ">From", in which case the ">" has been inserted to prevent the mail reader from thinking that the "From " is the start of a new mail.
The signature should start with "-- \r\n", though there is a very good chance that the trailing space will be missing.

Version 3 of OSBF-Lua has a mail-parsing library that will handle the MIME and split a message into its MIME parts and so on. I currently have a mess of Lua scripts that do
stuff like ignore most non-text attachments, prefer plain text to HTML, and so on. (I also wrap long lines to 80 characters while trying to preserve quoting.)
As far as removing previously quoted mail, the suggestions above are all good (you must subscribe to some ill-mannered mailing lists).
Removing disclaimers reliably is probably going to be hard. My first cut would be simply to maintain a library of disclaimers that would be stripped off the end of each mail message; I would write a script to make it easy for me to add to the library. For something more sophisticated I would try some kind of machine learning.
I've been working on spam filtering since Feb 2007 and I've learned that anything to do with email is a mess. A good rule of thumb is that whatever you want to do is a lot harder than you think it is :-(

Given your question "Is it possible to programmatically ‘clean’ emails?", I'd answer "No, not reliably".
The danger you face isn't really a technological one, but a sociological one.
It's easy enough to spot, and filter out, some aspects of the messages - like images. Filtering out signatures and disclaimers is, likewise, possible to achieve (though more of a challenge).
The real problem is the cost of getting it wrong.
What happens if your filter happens to remove a critical piece of the message? Can you trace it back to find the missing piece, or is your filtering desctructive? Worse, would you even notice that the piece was missing?
There's a classic comedy sketch I saw years ago that illustrates the point. Two guys working together on a car. One is underneath doing the work, the other sitting nearby reading instructions from a service manual - it's clear that neither guy knows what he's doing, but they're doing their best.
Manual guy, reading aloud: "Undo the bold in the centre of the oil pan ..." [turns page]
Tool guy: "Ok, it's out."
Manual guy: "... under no circumstances."

If you creating your own application i'd look into Regex, to find text and replace it. To make the application a little nice, i'd create a class Called Email and in that class i have a property called RAW and a property called Stripped.
Just some hints, you'll gather the rest when you look into regex!

SigParser has an assembly you can use in .NET. It gives you the body back in both HTML and text forms with the rest of the stuff stripped out. If you give it an HTML email it will convert the email to text if you need that.
var parser = new SigParser.EmailParsing.EmailParser();
var result = await parser.GetCleanedBodyAsync(new SigParser.EmailParsing.Models.CleanedBodyInput {
FromEmailAddress = "john.smith#example.com",
FromName = "John Smith",
TextBody = #"Hi Mark,
This is my message.
Thanks
John Smith
888-333-4434"
});
// This would print "Hi Mark,\r\nThis is my message."
Console.WriteLine(result.CleanedBodyPlain);