Got it -- Totally misunderstood where to put mail_crypt. Here is what I did:
try this configuration for your main.cf
relayhost = [smtp.gmail.com]:587
smtp_use_tls = yes
smtp_sasl_auth_enable = yes
smtp_sasl_security_options = noanonymous
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt
smtp_sasl_mechanism_filter = login
assuming you have all the other configs done ...
I have the same kind of issue.
After updating from Alpine container 3.12.3 to 3.13.3 my postfix with sasl did not work. First it could not read my sasldb2 file at all - I had to recreate it with saslpasswd2. sasldblistusers2 then worked.
But postfix does not work with this. I get this error message:
SASL authentication failure: Couldn't fetch entry from /...