Immediately after an update, trying to send mail (from mutt) gives me this: 

2017-07-02 20:42:32 1dRklM-0000VN-1O Cannot open main log file
"/var/log/exim/main.log": Permission denied: euid=496 egid=496
2017-07-02 20:42:32 1dRklM-0000VN-1O Failed to create spool file
/var/spool/exim/input//1dRklM-0000VN-1O-D: Permission denied
2017-07-02 20:42:32 1dRklM-0000VN-1O Cannot open main log file
"/var/log/exim/main.log": Permission denied: euid=496 egid=496
exim: could not open panic log - aborting: see message(s) above

I can't really do much investigation right now - I need to roll back...