The Mail::Box::Parser::Perl implements parsing of messages in Perl. This may be a little slower than the C based parser Mail::Box::Parser::C, but will also work on platforms where no C compiler is available.
When header errors are detected, the parsing of the header will be stopped. Other header lines will become part of the body of the message. Set this flag to have the erroneous line added to the previous header line.
When a message parser starts working, it takes size and modification time of the file at hand. If the folder is written, it checks wether there were changes in the file made by external programs.
Calling Mail::Box::update() on a folder before it being closed will read these new messages. But the real source of this problem is locking: some external program (for instance the mail transfer agent, like sendmail) uses a different locking mechanism as you do and therefore violates your rights.
Fatal error: the specific package (or one of its superclasses) does not implement this method where it should. This message means that some other related classes do implement this method however the class at hand does not. Probably you should investigate this and probably inform the author of the package.
While parsing a message from the specified source (usually a file name), the parser found a syntax error. According to the MIME specification in the RFCs, each header line must either contain a colon, or start with a blank to indicate a folded field. Apparently, this header contains a line which starts on the first position, but not with a field name.
By default, parsing of the header will be stopped. If there are more header lines after the erroneous line, they will be added to the body of the message. In case of new(fix_headers) set, the parsing of the header will be continued. The erroneous line will be added to the preceding field.