GHSA-F2HQ-32VH-53CC postal-mime: Quadratic CPU consumption when decoding a header of many joinable RFC 2047 base64 encoded words

Impact Decoding a header that holds a long run of joinable RFC 2047 base64 encoded words, such as =?utf-8?B?QUJD?= repeated tens of thousands of times in a Subject, From, To, a filename or a description, took time quadratic in the number of words. The join check ran a regex over the text joined s...