Thunderbird fails to read signature even on complain mode, because AFAIK complain mode does still mediate `deny` clauses:
sudo sysdig "fd.name contains signature"271543 15:19:14.386997890 6 thunderbird (3680) < open fd=-13(EACCES) name=/home/vincas/.signature-...@example.com flags=1(O_RDONLY) mode=0
I guess there will be something in `abstractions/private-files` or similar, gonna check all deny rules.
