On cPanel Linux server one can use following command to find the latest Sent mail file. The email file that cpanel account sent most latelly.

find /home/cpanelusername/mail -path "*Sent*" -iname "*$(hostname)*" | head -n1 | sort -nr

example output:

/home/cpanelusername/mail/domain.info/mark/.Sent/cur/1416344681.M505606P12954.fqdnhostname.domain.tld,S =650,W=677:2,S