An excessive memory use issue (CWE-770) exists in Email-MIME, before version 1.954, which can cause denial of service when parsing multipart MIME messages. The patch set (from 2020 and 2024) limits excessive depth and the total number of parts.
Changes for version 1.939 - 2017-01-14 (TRIAL RELEASE)
do not decode MIME headers known to be never encoded (Pali Rohár)
...and that includes the Downgraded-* headers (Pali Rohár)
Changes for version 1.938 - 2017-01-01 (TRIAL RELEASE)
numerous small fixes to header encoding (thanks, Pali Rohár) for more details see https://github.com/rjbs/Email-MIME/pull/32
When a single-part content type has been provided with multiple parts, the user is now warned that the type has been changed to multipart/mixed. This helps catch typos like "mutlipart/alternative".