C# Library for moving CSS to inline style attributes, to gain maximum E-mail client compatibility.

string htmlSource = File.ReadAllText(@"C:\Workspace\testmail.html");

var result = PreMailer.MoveCssInline(htmlSource);

result.Html 		// Resultant HTML, with CSS in-lined.
result.Warnings 	// string[] of any warnings that occurred during processing.

string htmlSource = File.ReadAllText(@"C:\Workspace\testmail.html");

var pm = new PreMailer(htmlSource);
// Optional to add analytics tags
pm.AddAnalyticsTags(source, medium, campaign, content, domain = null);

var result = pm.MoveCssInline(
    removeStyleElements: false,
    ignoreElements: "#ignore",
    preserveMediaQueries: true
);

result.Html       // Resultant HTML, with CSS in-lined.
result.Warnings   // List<string> of any warnings that occurred during processing.

The following options can be passed to the PreMailer.MoveCssInline method to configure its behavior:

• baseUri(Uri = null) - Base URL to apply to link elements with href values ending with .css.
• removeStyleElements(bool = false) - Removes elements that were used to source CSS (currently, only style is supported).
• ignoreElements(string = null) - CSS selector of element(s) not to inline. Useful for mobile styles (see below).
• css(string = null) - A string containing a style-sheet for inlining.
• stripIdAndClassAttributes(bool = false) - True to strip ID and class attributes.
• removeComments(bool = false) - True to remove comments, false to leave them intact.
• customFormatter(IMarkupFormatter = null) - Custom formatter to use for the HTML output.
• preserveMediaQueries(bool = false) - If true and removeStyleElements is true, it will preserve media queries in the style node while removing other CSS, instead of removing the entire style node.
• useEmailFormatter(bool = false) - If true, empty HTML tags will be preserved as full tags instead of being converted to self-closing tags, and HTML entities like © will be preserved.

Sometimes it's handy to reference external style sheets with a <link href="..." /> element. PreMailer will download and use external style sheets as long as the value of href ends with .css.

Both absolute and relative URLs are supported. If the URL is relative, you must specify the baseUri parameter in either the constructor, or when calling the static MoveCssInline method.

<link /> elements that match the ignoreElements selector won't be downloaded.

If you want to apply mobile styles to your e-mail, you should put your mobile specific styles in its own style block that targets the appropriate devices using media queries.

But since you cannot know by the time of sending an e-mail whether or not it will be viewed on a mobile device, the style block that targets mobile devices should not be inlined!

To ignore a style block, you need to specify an ignore selector when calling the MoveCssInline method, like this:

var result = PreMailer.MoveCssInline(input, false, ignoreElements: "#ignore");

Alternatively, you can use the preserveMediaQueries parameter to keep your media queries while removing other styles:

var result = PreMailer.MoveCssInline(input, removeStyleElements: true, preserveMediaQueries: true);

And your mobile specific style block should have an ID of ignore:

<style type="text/css" id="ignore">.target { width: 1337px; }</style>

Premailer looks for the use of CSS attributes prefixed with -premailer and will proxy the value through to the DOM element as an attribute.

For example

table {
    -premailer-cellspacing: 5;
    -premailer-width: 500;
}

will make a table element render as

<table cellspacing="5" width="500">

The AddAnalyticsTags method can be used to add Google Analytics tracking parameters to links in your HTML:

var pm = new PreMailer(htmlSource);
pm.AddAnalyticsTags(
    source: "newsletter",       // utm_source parameter
    medium: "email",            // utm_medium parameter
    campaign: "summer_sale",    // utm_campaign parameter
    content: "logo_link",       // utm_content parameter
    domain: "example.com"       // Optional: only add tags to links matching this domain
);

This will append ?utm_source=newsletter&utm_medium=email&utm_campaign=summer_sale&utm_content=logo_link to all links, or to links matching the specified domain if provided.

The Document property provides access to the underlying IHtmlDocument object, allowing you to perform custom DOM manipulation before inlining CSS:

using(var pm = new PreMailer(html)){
  var document = pm.Document;

  // Use AngleSharp to process document before moving css inline...
  
  var result = pm.MoveCssInline();
}

This is useful for advanced scenarios where you need to modify the HTML structure before applying CSS.

• Pseudo classes/elements which not supported by external dependencies, or doesn't make sense in email, will be ignored and logged to the InlineResult.Warnings collection.

NuGet: PreMailer.Net

• martinnormark
• robcthegeek

Among others

PreMailer.Net is available under the MIT license. See the LICENSE file for more info.