I am also experiencing on openSUSE Factory more or less what is described here:

https://bugs.archlinux.org/task/35627

Local mail sending by regular users does not work, the journal contains:
cron[1893]: postdrop: warning: mail_queue_enter: create file
maildrop/463330.14336: Permission denied
postfix/postdrop[14336]: warning: mail_queue_enter: create file
maildrop/463330.14336: Permission denied
cron[1893]: postdrop: warning: mail_queue_enter: create file
maildrop/606362.15354: Permission denied
postfix/postdrop[15354]: warning: mail_queue_enter: create file
maildrop/606362.15354: Permission denied

In our case, the binaries should be owned by the group maildrop instead of
postfix (as in the Arch Linux report), according to:

root@f1:~# postfix check
postfix/postfix-script: warning: not owned by group maildrop:
/usr/sbin/postqueue
postfix/postfix-script: warning: not owned by group maildrop:
/usr/sbin/postdrop
postfix/postfix-script: warning: not set-gid or not owner+group+world
executable: /usr/sbin/postqueue
postfix/postfix-script: warning: not set-gid or not owner+group+world
executable: /usr/sbin/postdrop

Manually applying these ownership/mode changes works around the problem.

ben@f1:~$ rpm -qi postfix
Name        : postfix
Version     : 2.11.0
Release     : 7.1
Architecture: x86_64
Install Date: Thu 18 Sep 2014 04:26:41 AM PDT
Group       : Productivity/Networking/Email/Servers
[...]