Cannot send or receive email ('Message not sent. Server replied:)

[Numicus]

It's a fresh install yes, I changed the nameserver, maybe it has got something to do with that.

Following files:

/etc/hosts:
# 'hosts' file configuration.
127.0.0.1 srv015-stb.zennid.nl.local localhost
77.243.232.64 srv015-stb.zennid.nl srv015-stb
::ffff:77.243.232.64 srv015-stb.zennid.nl srv015-stb
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

/etc/host.conf:
multi on

/etc/hostname:
srv015-stb

/etc/resolv.conf:
search zennid.nl
nameserver 217.170.1.1