[exim] Run expansion with a tainted variable

Hello,

I have a run expansion using a tainted variable:

condition = ${run{/usr/bin/spfquery.mail-spf-perl \
               --ip $sender_host_address \
               --scope mfrom \
               --identity $sender_address} \
               {no}{${if eq {$runrc}{1}{yes}{no}}}}

Is this usage of $sender_address safe? And if not, what would I do to
make it safe?

Thanks,
Dominic.

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