The IMTA often receives from misconfigured or incompliant mailers and SMTP clients addresses that do not contain a domain name. IMTA attempts to make such addresses legal before allowing them to pass further. IMTA does this by appending a domain name to the address (for example, appends @acme.com to mrochek). In the case of the SMTP server, however, the two logical choices for the domain name are:
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Local host name |
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Remote host name reported by the client SMTP |
Either of these two choices is likely to be correct, as both may occur operationally with some frequency. The use of the remote host's domain name is appropriate when dealing with improperly configured SMTP clients. The use of the local host's domain name is appropriate when dealing with a lightweight remote mail client such as a POP or IMAP client that uses SMTP to post messages.
The best that IMTA can do is to allow the choice to be made on a channel-by-channel basis. The remotehost channel keyword specifies that the remote host's name should be used. The noremotehost channel keyword specifies that the local host's name should be used. noremotehost is the default.
The switchchannel keyword as described, in the preceding section, "Select an Alternate Channel for Incoming Mail (switchchannel, allowswitchchannel, noswitchchannel)" can be used to associate incoming SMTP connections with a particular channel. This facility can be used to group remote mail clients on a channel where they can receive proper treatment. Alternatively, it is simpler to deploy standards-compliant remote mail clients (even if a multitude of incompliant clients are in use) rather than attempting to fix the network-wide problem on your IMTA hosts.