[EXIM] Help I'm stuck behind a firewall

My hostname is nbeckerpc.hns.com. You can't look it up from outside
hns.com.

I tried at first the default primary_hostname, but some mailers refuse
my connection. I think that's because the name given in the HELO was
not something that could be looked up in the DNS.

I found that setting primary_hostname to hns.com was a workaround.

Is this the best (only) solution?

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