[Dovecot] 143 STARTTLS/ 993 SSL/TLS query

I'm testing my new dovecot server with Thundirbird

I can have it working on port 143 with STARTTLS, or on port 993 with SSL/TLS

my uderstanding is that on 993 I get encrypted 'password and mail transfer' (yes ?)

so what happens if I use 143 with STARTTLS, is that equivalent to port 993 if STARTTLS is used ?

thanks for any insights..

-- Voytek