Re: Is there a way to avoid using IPv6 in outgoing SMTP connections?

On 19/06/2026 11:47, Fabio Muzzi via Exim-users wrote:
> Hi, I have issues sending email using ipv6 because my VPS provider (OVH) 
> allocates a single ip /128 to each vm, and of course a lot of neighbor 
> addresses (inside the /64) are in blacklist, so I'm in blacklist too. 
> This is a known problem since forever but they just don't fix it. It 
> would require a major overhaul of the v6 allocations for the whole 
> infrastructure.
> 
> The obvious solution is to not use ipv6 for SMTP sending (but I can use 
> it for receiving, no problem there).
> 
> So I tried to set "interface = MY V4 ADDRESS" in the smtp transport config.
> 
> It does not work, it still uses both v4 and v6.
> 
>  From what I have understood from documentation, it's by design, it's 
> not a bug. If I select a v4 address and not a v6 address, the logic of 
> address selection will happily use the first available v6 address 
> because I have not chosen a specific v6 address to use.
> 
> This takes me to the point: is there no way of telling Exim to use only 
> ipv4 in outgoing smtp connections, apart from disabling v6 completely in 
> Exim (with disable_ipv6=true), thus rejecting also incoming v6 smtp 
> connections?

In addition to 'interface =' in the transport, try using

  ignore_target_hosts = <; 0::0/0

in the router so that IPv6 addresses are discarded. See
https://exim.org/exim-html-current/doc/html/spec_html/ch-generic_options_for_routers.html

-- 
Eduardo M KALINOWSKI
[email protected]

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