[Exim] TCP port "smtp" not defined error

Hi,

I am getting this error, and I am not so sure what could be causing it

T=remote_smtp defer (-1): TCP port "smtp" is not defined for remote_smtp
transport

I cannot send mail to any remote host. The smtp port is listed in
/etc/services and the remote transport looks fine:

Using exim-4.34-0

Thanks, luke.