#### 5.8.6 The editheader extension ¶

The `editheader` extension complies with RFC 5293. It provides the following actions:

Action: addheader `[:last] field-name(string) value(string)` ¶

  Adds a header field to the existing message header. By default the header is inserted at the beginning of the header list. If the tag `:last` is specified, it is appended at the end.

Action: deleteheader" `[:index fieldno(number) :last] [comparator] [match-type] field-name(string) [value-patterns(string-list)]` ¶

  Deletes occurrences of the header field matching the criteria.

  The value-patterns, if specified, determines which occurrences of the header fielde to delete. If not supplied, comparator and match-type are silently ignored.

  If ‘`:index fieldno`’ is specified, only the numbered occurrence of the named header field will be matched (header numbering begins at 1), If `:last` is specified, the count is backwards; 1 denotes the last named header field, 2 the second to last, and so on. The counting happens before the value-patterns match, if any. Thus, e.g. the action

      deleteheader :index 1 :contains "Delivered-To" "bob@example.com";

  would delete the first ‘`Delivered-To`’ header field if it contains the string ‘`bob@example.com`’.