> I wasn't sure what to put in for the HELO statement (I found out that at > SMTP start up the host name is DEVVM and domain name is muhc.mcgill.ca) so > at first I wasn't sure so I put in "HELO DEVVM.muhc.mcgill.ca" and then > did a SENDFILE to user SMTP. > > It didn't seem to get delivered so I tried again with "HELO > muhc.mcgill.ca" > I got a response back from that one after a couple of minutes (I think it > was from that one). > > Anyways it appeared both got through but which one is the correct one and > does it make a difference?
The HELO line identifies the hostname of submitting client, or whomever they claim to be. Both are technically permitted, although VM SMTP does not verify the validity of the domain name supplied on the HELO. (This is one of the longstanding flaws in at least the older versions of VM SMTP -- it should at least flag it as a bogus HELO.) > I was also wondering how VM user smtp knows which client mail server to > contact? For TCP/IP for VSE, I needed to specify the actual IP address of > the server but not for VM, I believe. The argument to the RCPT envelope command is parsed as <[EMAIL PROTECTED]>. SMTP MTAs process only the RFC 821 envelope -- the part up to the DATA component of the transaction. The RFC 822 bits (the stuff in the body of the mail) are pretty much an opaque payload. The MTA attempts to resolve MX records for destination.server from above, then tries to resolve A records for destination.server. If neither are available, the host is unresolvable and delivery fails.
