MailMate before 1.11.3 mishandles a suspicious HTML/MIME structure in a signed/encrypted email.
packetstormsecurity.com/files/152703/Johnny-You-Are-Fired.html
seclists.org/fulldisclosure/2019/Apr/38
www.openwall.com/lists/oss-security/2019/04/30/4
github.com/RUB-NDS/Johnny-You-Are-Fired
github.com/RUB-NDS/Johnny-You-Are-Fired/blob/master/paper/johnny-fired.pdf
updates.mailmate-app.com/release_notes