N can be 224, 256 (default), 384, 512.
With GnuTLS 3.5.0 or later, only.
+ 5. Facility for named queues: A commandline argument can specify
+ the queue name for a queue operation, and an ACL modifier can set
+ the queue to be used for a message. A $queue_name variable gives
+ visibility.
+
+ 6. The CHUNKING ESMTP extension from RFC 3030. May give some slight
+ performance increase and network load decrease. Main config option
+ chucking_advertise_hosts for control.
+
Version 4.87
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