IMAP STARTTLS sniff tool

Hi all. 
We managed succesfully to sniff inside POP3S, SMTPS, IMAPS & HTTPS tunnels using arpspoof, iptables & sslsplit to make 
MITM. 
Now we want to sniff inside STARTTLS tunnels (specifically IMAP) but unfortunately sslsplit doesn't supports STARTTLS. 
Is there/do you know another SSL/TLS tool supporting IMAP over STARTTLS to make MITM? 

Many thanks 
B. 

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