Including html tags in Email Subject [PHP]

Question

Using headers, the html tags would be parsed in Mail Content/Body, But what if we want to have some html tags in Mail Subject. Is there any way out for this

Answer 1

Even if you put html tags in mail subject, the mail client won't render it as html

As per email RFC, email subject can't have a content type

From rfc http://www.w3.org/Protocols/rfc822/

3.1.2. STRUCTURE OF HEADER FIELDS

Once a field has been unfolded, it may be viewed as being composed of a field-name followed by a colon (":"), followed by a field-body, and terminated by a carriage-return/line-feed. The field-name must be composed of printable ASCII characters (i.e., characters that have values between 33. and 126., decimal, except colon). The field-body may be composed of any ASCII characters, except CR or LF. (While CR and/or LF may be present in the actual text, they are removed by the action of unfolding the field.)
Certain field-bodies of headers may be interpreted according to an internal syntax that some systems may wish to parse. These fields are called "structured fields". Examples include fields containing dates and addresses. Other fields, such as "Subject" and "Comments", are regarded simply as strings of text.

Note:

Any field which has a field-body that is defined as other than simply <text> is to be treated as a structured field.
Field-names, unstructured field bodies and structured field bodies each are scanned by their own, independent "lexical" analyzers.

3.1.3. UNSTRUCTURED FIELD BODIES

For some fields, such as "Subject" and "Comments", no structuring is assumed, and they are treated simply as <text>s, as in the message body. Rules of folding apply to these fields, so that such field bodies which occupy several lines must therefore have the second and successive lines indented by at least one LWSP-char.