Authentication problems due to file ownership issue.

[dovecot at ptld.com]

> Oct 03 20:19:52 auth: Error: net_connect_unix(auth-worker) in directory 
> /run/dovecot failed: Permission denied (euid=5000(vmail) 
> egid=5000(vmail) missing +r perm: /run/dovecot/auth-worker, dir owned 
> by 0:0 mode=0755)

> I set this about an hour ago, then applied some security patches and 
> restarted

Files and directories inside of /run/ are created every time you reboot 
the server. If you manually change the owner or permissions it will only 
stay that way until next reboot. You have to edit config settings for 
the service in question for how you want those directories / files 
created on reboot. I do not know how to do that in ubuntu but in RHEL 
you edit (or create) config files in /etc/tmpfiles.d/

Package installed default on RHEL
    /usr/lib/tmpfiles.d/dovecot.conf
    "d /var/run/dovecot 0755 root dovecot -"

Not sure what you are trying to do, but another option might be give 
user vmail dovecot group access so vmail can access files with a dovecot 
group read permission.
     usermod -a -G dovecot vmail