By bidirectional pipes I mean a situation where you start a subordinateprogram and both write to its standard input and read from its standardoutput. There are a fair number of programs that are programmed like thefollowing pseudo-code:

to, from = pipecmd("subprogram", "rw")write(to, stuff)reply = read(from)

People write these programs, test them a bit, start using them, havethem work, and then one day wake up to discover that their program has

The Exim documentation is a little silent on howExim determines the retry time for local deliveries. Since I spent todaylooking into this, I might as well write up what I've learned.

Exim's retry rules are based on matching patterns against 'the failinghost or address' (as the documentation puts it); call this the retrykey. For local deliveries, it turns out that the retry key is the fulladdress (including any local part prefixes or suffixes) that is handedto the transport

This week, we:

• got 11,909 messages from 265 different IP addresses.
• handled 26,934 sessions from 2,995 different IP addresses.
• received 297,885 connections from at least 101,029 different IPaddresses.
• hit a highwater of 16 connections being checked at once.

Volume is a bit up from last week . Lookingat the numbers I am reminded of how striking the number of differentIP addresses is

First, some terminology. A top level address is an address that amessage starts out being sent to; for example, every (accepted) RCPTTO in SMTP creates a top level address for the message. A destination is a place that a message is ultimately going to be delivered to, andmay include things like files. A top level address may turn into morethan one destination through means like .forward files, aliases, andmailing list files. At a conceptual level, all MTAs have two main jobs