Add environment variable for logfile for msmtp

Hi,
I need to troubleshoot email being sent from another docker container using the sending mail from msmtp. I'm asking if it would be possible to add an environment variable for logfile for msmtp.
In the configuration file, it's possible to define the logfile by adding this line:

logfile        /var/log/msmtp

But in this docker, I don't see a way to specify this variable.
Thanks.