libs/comverp.c in Courier MTA before 0.53.2 allows attackers to cause a denial of service (CPU consumption) via unknown vectors involving usernames that contain the "=" (equals) character, which is not properly handled during encoding.

Multiple buffer overflows in (1) iso2022jp.c or (2) shiftjis.c for Courier-IMAP before 3.0.0, Courier before 0.45, and SqWebMail before 4.0.0 may allow remote attackers to execute arbitrary code "when Unicode character is out of BMP range."