postfix/qmgr error - connect to private/dovecot No such file or directory

I have a Ubuntu 18.0.4 bionic with postfix and dovecot and dovecot-mysql installed. Receiving the errors shown on lines 1 and 2:

Jul  4 15:58:05 mailer postfix/qmgr[11870]: warning: connect to transport private/dovecot: No such file or directory
Jul  4 15:58:05 mailer postfix/error[1463]: EDCC317B342: to=<[email protected]>, relay=none, delay=0.09, delays=0.07/0.01/0/0.01, dsn=4.3.0, status=deferred (mail transport unavailable)
Jul  4 15:58:05 mailer postfix/smtpd[1456]: disconnect from mail-io1-f44.google.com[209.85.166.44] ehlo=1 mail=1 rcpt=1 data=1 quit=1 commands=5

I do not understand the message warning: connect to transport private/dovecot: No such file or directory; is private/dovecot the file/folder it's referring to or is it a process? I've done a grep through the entire /etc/postfix file to figure out what private/dovecot is, and don't see the pattern.

UPDATE: by trial and error I have found that private/{process_name} comes from the postfix main.cf setting virtual_transport = {process_name} - it can be dovecot or mailman or whatever - but why am I still getting the no such file or directory message..

Answer: there are two parts to this.

1) private/{process_name} actually references /var/spool/postfix/private/{process_name} which you can check to see if it's there. I discovered this from https://www.howtoforge.com/postfix-dovecot-warning-sasl-connect-to-private-auth-failed-no-such-file-or-directory and extrapolated from that path..

[...] (sample code for a process mapping)
client {
   path = /var/spool/postfix/private/auth
   mode = 0660
   user = postfix
   group = postfix
}
[...]

2) after that I realized it was a user error (myself), and with service postfix restart the process showed.