Thanks Jeremy! That was it.
For anyone who might have the same issue:
The solution was to add 'disable_ipv6=true' to the config and reload
config.
On Apr 24 at 01:52 PM, Jeremy Harris via Exim-users said thus:
> On 23/04/2019 15:04, MaDhAt2r via Exim-users wrote:
>> 2019-04-23 08:43:19.559 [23071] 1hIvhX-0005wV-4z H=aspmx.l.google.com [2a00:1450:4013:c00::1a]:25 Cannot assign requested address
>
> You have some problem with IPv6 addressing on your system, is
> a reasonable probability.
> --
> Cheers,
> Jeremy
>
> --
> ## List details at https://lists.exim.org/mailman/listinfo/exim-users
> ## Exim details at http://www.exim.org/
> ## Please use the Wiki with this list - http://wiki.exim.org/
