OOT: Mail rejected with bogus helo

Julian Field MailScanner at ecs.soton.ac.uk
Thu Apr 17 19:04:16 IST 2008

Glenn / Matt,

Do you fancy taking this never-ending thread off-list please? It 
deserves an awful lot of O's in its "OT" and I'm sad to say it descended 
below boredom threshold for many of the rest of us a long time ago :-)

If you ever come to an agreement, please feel free to post a summary :-)

Thanks guys!
Jules. :-)

Matt Kettler wrote:
> Glenn Steen wrote:
>>>  Also, this thread is about using an IP as a HELO, which is NOT a 
>>> malformed
>>> HELO per the RFCs. Therefore it is still against the RFCs to refuse 
>>> mail
>>> because the HELO is an IP address.
>> Are you thinking "a plain word that looks like an IP address" then?
>> Cause I'm pretty sure (boy am I going to get it... Haven't reread the
>> exact wording:-) that the demand is for Ip address literals, like
>> Steve points out, not a domain name looking like an IP address...
>> Oh well.
> Erm, I'm not sure what difference you're implying exists between "a 
> plain word that looks like an IP address" and an "IP address literal". 
> I'm also not sure what you mean by "a domain name looking like an IP 
> address".
> The HELO string in question was "", sans quotes, which 
> matches RFC2821's definition of IPv4-address-literal in section 4.1.3, 
> which is in turn a sub-type of address-literal in 4.1.2. This makes it 
> 100% valid syntactically.
> Of course, exposing a non-routable IP as a HELO is obviously bogus 
> information, but it is not syntactically invalid. Thus, blocking based 
> on it is technically against the RFCs. However, I'd expect some sites 
> will block this, since the information presented is obviously invalid.


Julian Field MEng CITP CEng
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