Am I wrong to use 127.0.0.1 as my IP Address

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Question

The admin guide in section 7.2 Incoming Mail says “If you are only using one domain (the root domain), you don’t have to make an entry here and the localhost value (127.0.0.1) will be used by default.” Am I wrong to use 127.0.0.1? I am only using one domain.

Answer

127.0.0.1 is the “loopback” address and always refers to the local machine. If you are standalone and not networked this is fine.

If you are networked you must use the machine’s real IP address. The problem is, every machine thinks it’s 127.0.0.1, so it’s no good as an idenitifier. For example, mail to another server would send 127.0.0.1 as the source IP and messages would appear to come from “localhost” instead of the real machine name – this might give you strange problems sending mail esp if the remote server attempted to authenticate your machine in a DNS.

Use the primary IP address of the machine.

Keywords:localhost, IP Address, 127.0.0.1

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