adduser: The user `_rmilter' already exists. Exiting.

[Safari77]

I get this on ubuntu when doing "apt upgrade"

The following partially installed packages will be configured:
  rmilter 
No packages will be installed, upgraded, or removed.
0 packages upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 0 B of archives. After unpacking 0 B will be used.
Setting up rmilter (1.9.2-2~xenial) ...
adduser: The user `_rmilter' already exists. Exiting.
dpkg: error processing package rmilter (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 rmilter
E: Sub-process /usr/bin/dpkg returned an error code (1)
Failed to perform requested operation on package.  Trying to recover:
Setting up rmilter (1.9.2-2~xenial) ...
adduser: The user `_rmilter' already exists. Exiting.
dpkg: error processing package rmilter (--configure):
 subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
 rmilter