Under consideration in the next major version of maildrop is the replacement of maildrop's internal regular expression pattern match with the functionality provided by the PCRE library (http://www.pcre.org). PCRE is now widely used in many places. A preliminary review shows that PCRE will be able to support all of maildrop's functionality except for the "w" pattern option. With PCRE, the "w" option would require the entire message to be loaded into memory. Maildrop does not load large messages into memory, and this would not be desirable. Therefore, adoption of PCRE will require dropping the "w" option.

The current plan is to have a transition period, with optional fallback to the old regular expression pattern matching engine. The default configuration will use PCRE, and an explicit setting will be required to fallback to the old engine.