PMDF System Manager's Guide

Firewall considerations for additional channel keywords:

• The deferred channel keyword is discussed in Section 2.3.4.19; note that use of this keyword allows users to use the PMDF system's e-mail disk space as an extension of their own disk space. The default behavior of nodeferred is likely particularly appropriate behavior for an e-mail firewall if you are concerned about preventing a denial of service attack on your disk space.
• The maxprocchars channel keyword causes PMDF to not bother processing addresses in headers over the specified number of characters; in such a case PMDF passes the unprocessed headers through unchanged. See Section 2.3.4.78 for details.
• On OpenVMS, the network rightslist identifier requires users of the channel to have the NETMBX privilege; see Section 2.3.4.89 for details.
• The nonurgentblocklimit, normalblocklimit, and urgentblocklimit channel keyword can be used to set thresholds for when to downgrade message priority. Message priority, in turn, can affect whether PMDF attempts to send a message immediately, or whether PMDF lets the message wait until the next time the PMDF periodic delivery job runs. Depending upon your needs and circumstances, having large messages wait on the firewall system until a periodic job runs can be either beneficial, by not using resources that could be used to send small messages immediately, or can expose your firewall system to the potential for getting its disk space "clogged up" with pending large messages in between runs of the periodic job.
• The nox_env_to channel keyword, which is the default, ensures that no X-Envelope-to: headers are put on messages. If you are using centralized naming, this is likely a particularly appropriate default. The x_env_to channel keyword, on the other hand, requests that PMDF include an X-Envelope-to: header.