At 01:50 26-01-2009, Paul Smith wrote:
I have a 'common' situation in mind. Whether you like it or not, it is
There is a small business who has bought Microsoft SBS. They are running
Microsoft Exchange with the POP3 connector over a dynamic IP ADSL. They
have Exchange set up for direct sending, with fallback to their ISP's
smarthost. They don't want to change to always use their ISP's smarthost
because that has long delays in sending.
What are they supposed to use for the EHLO parameter if it is important
enough to mean the difference between delivery or not?
The parameter should be the SMTP client's identity. From RFC 5321:
"The domain name given in the EHLO command MUST be either a primary
host name (a domain name that resolves to an address RR) or, if
the host has no name, an address literal, as described in
Section 4.1.3 and discussed further in the EHLO discussion of
You may experience delivery issues sending mail from a connection
using a dynamic IP address.