Since it took me all morning to figure out how to get my email working again, FYI:
dovecot imap stopped working after the du with the openssl update of these packages:openssl:amd64 (1.1.0h-4, 1.1.1~~pre9-1),
libssl-dev:amd64 (1.1.0h-4, 1.1.1~~pre9-1),
libssl-doc:amd64 (1.1.0h-4, 1.1.1~~pre9-1),
libssl1.1:amd64 (1.1.0h-4, 1.1.1~~pre9-1),
The error in my system logs was:dovecot imap-login: Error: Failed to initialize SSL server context: Can't load SSL certificate: error:140AB18F:SSL routines:SSL_CTX_use_certificate:ee key too small:
The solution was to make a new self signed certificate with a key length of 4096 (it might have worked with 2048 but I didn't experiment, the original 1024 I had was too small)
openssl genrsa -out dovecot.key 4096
If there's interest I can outline the step by step process to create a self signed certificate.