class email.policy.EmailPolicy(**kw)  
This concrete Policy provides behavior that is intended to be fully compliant with the current email RFCs. These include (but are not limited to) RFC 5322, RFC 2047, and the current MIME RFCs. This policy adds new header parsing and folding algorithms. Instead of simple strings, headers are str subclasses with attributes that depend on the type of the field. The parsing and folding algorithm fully implement RFC 2047 and RFC 5322. The default value for the message_factory attribute is EmailMessage. In addition to the settable attributes listed above that apply to all policies, this policy adds the following additional attributes:  New in version 3.6: 1   
utf8  
If False, follow RFC 5322, supporting non-ASCII characters in headers by encoding them as “encoded words”. If True, follow RFC 6532 and use utf-8 encoding for headers. Messages formatted in this way may be passed to SMTP servers that support the SMTPUTF8 extension (RFC 6531). 
  
refold_source  
If the value for a header in the Message object originated from a parser (as opposed to being set by a program), this attribute indicates whether or not a generator should refold that value when transforming the message back into serialized form. The possible values are:  
none all source values use original folding  
long source values that have any line that is longer than max_line_length will be refolded  
all all values are refolded.   The default is long. 
  
header_factory  
A callable that takes two arguments, name and value, where name is a header field name and value is an unfolded header field value, and returns a string subclass that represents that header. A default header_factory (see headerregistry) is provided that supports custom parsing for the various address and date RFC 5322 header field types, and the major MIME header field stypes. Support for additional custom parsing will be added in the future. 
  
content_manager  
An object with at least two methods: get_content and set_content. When the get_content() or set_content() method of an EmailMessage object is called, it calls the corresponding method of this object, passing it the message object as its first argument, and any arguments or keywords that were passed to it as additional arguments. By default content_manager is set to raw_data_manager.  New in version 3.4.  
 The class provides the following concrete implementations of the abstract methods of Policy:  
header_max_count(name)  
Returns the value of the max_count attribute of the specialized class used to represent the header with the given name. 
  
header_source_parse(sourcelines)  
The name is parsed as everything up to the ‘:’ and returned unmodified. The value is determined by stripping leading whitespace off the remainder of the first line, joining all subsequent lines together, and stripping any trailing carriage return or linefeed characters. 
  
header_store_parse(name, value)  
The name is returned unchanged. If the input value has a name attribute and it matches name ignoring case, the value is returned unchanged. Otherwise the name and value are passed to header_factory, and the resulting header object is returned as the value. In this case a ValueError is raised if the input value contains CR or LF characters. 
  
header_fetch_parse(name, value)  
If the value has a name attribute, it is returned to unmodified. Otherwise the name, and the value with any CR or LF characters removed, are passed to the header_factory, and the resulting header object is returned. Any surrogateescaped bytes get turned into the unicode unknown-character glyph. 
  
fold(name, value)  
Header folding is controlled by the refold_source policy setting. A value is considered to be a ‘source value’ if and only if it does not have a name attribute (having a name attribute means it is a header object of some sort). If a source value needs to be refolded according to the policy, it is converted into a header object by passing the name and the value with any CR and LF characters removed to the header_factory. Folding of a header object is done by calling its fold method with the current policy. Source values are split into lines using splitlines(). If the value is not to be refolded, the lines are rejoined using the linesep from the policy and returned. The exception is lines containing non-ascii binary data. In that case the value is refolded regardless of the refold_source setting, which causes the binary data to be CTE encoded using the unknown-8bit charset. 
  
fold_binary(name, value)  
The same as fold() if cte_type is 7bit, except that the returned value is bytes. If cte_type is 8bit, non-ASCII binary data is converted back into bytes. Headers with binary data are not refolded, regardless of the refold_header setting, since there is no way to know whether the binary data consists of single byte characters or multibyte characters.