Bugfix (introduced: Postfix 2.2): reject_multi_recipient_bounce
has been producing false rejects starting with the Postfix
2.2 smtpd_end_of_data_restrictons, and for the same reasons,
did the same with the Postfix 3.4 BDAT command. The latter
was reported by Andreas Schulze. File: smtpd/smtpd_check.c.

Bugfix (introduced: Postfix 3.0): LMTP connections over
UNIX-domain sockets were cached but not reused, due to a
cache lookup key mismatch. Therefore, idle cached connections
could exhaust LMTP server resources, resulting in two-second
pauses between email deliveries. This problem was investigated
by Juliana Rodrigueiro. File: smtp/smtp_connect.c.