(There are already some IPv6 only ISPs and I expect this will become more
viable over time. Should they have to set up IPv4 tunnels or ALGs for their
"legitimate" customers so those customers can still send email to IPv4
servers?)
No, they need a fixed IPv4 address with an MX so people on IPv4 servers
can send mail *to* them. As we've said a few dozen times already, one
mail server on one IPv4 address can handle a whole lot of mail for a whole
lot of people, both inbound and outbound.
The usual word for one-way mail to which one cannot reply is "spam".
Regards,
John Levine, johnl(_at_)taugh(_dot_)com, Taughannock Networks, Trumansburg NY
Please consider the environment before reading this e-mail. https://jl.ly
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