Get the value of the specified header from 'message' as a UTF-8 string.
Common headers are stored in the database when the message is
indexed and will be returned from the database. Other headers will
be read from the actual message file.
The header name is case insensitive.
The returned string belongs to the message so should not be
modified or freed by the caller (nor should it be referenced after
the message is destroyed).
Returns an empty string ("") if the message does not contain a
header line matching 'header'. Returns NULL if any error occurs.
Get the value of the specified header from 'message' as a UTF-8 string.
Common headers are stored in the database when the message is indexed and will be returned from the database. Other headers will be read from the actual message file.
The header name is case insensitive.
The returned string belongs to the message so should not be modified or freed by the caller (nor should it be referenced after the message is destroyed).
Returns an empty string ("") if the message does not contain a header line matching 'header'. Returns NULL if any error occurs.