• conf-channels: default number of channels increased to 4 (was 2). Now qmail offers 2 additional channels
  with respect to the 2 offered by default (local and remote). More info here.
• maxrcpt: error code changed to 452 due to RFC 4.5.3.1 (was 553). If DISABLE_MAXRCPT is defined it skips the check,
  otherwise outgoing messages from mailing lists would be rejected. (commit)