Cisco 1720, problem sending emails (SMTP)

Here is my configuration:

I manage to reach the internet as well as LAN from 2nd LAN. Cisco router makes routing and NAT (PAT)

Everything goes well except:

I can't ping a workstation on 2nd LAN from Cisco 1720 (but the same workstation manages to ping cisco interface?!?.....)

and also, I can't send emails bigger than about 30ko, sending process stops and I get a connection error.

here is my configuration:

etiam#sh run Building configuration...

Current configuration : 905 bytes ! version 12.2 service timestamps debug uptime service timestamps log uptime no service password-encryption ! hostname etiam ! ! memory-size iomem 20 ip subnet-zero ! ! ! ip audit notify log ip audit po max-events 100 ip ssh time-out 120 ip ssh authentication-retries 3 ! crypto mib ipsec flowmib history tunnel size 200 crypto mib ipsec flowmib history failure size 200 ! ! ! interface Ethernet0 ip address 192.168.0.226 255.255.255.0 no ip proxy-arp ip mtu 1490 ip nat outside full-duplex no cdp enable ! interface FastEthernet0 ip address 172.16.1.254 255.255.255.0 no ip proxy-arp ip nat inside speed auto full-duplex no cdp enable ! ip nat inside source list 1 interface Ethernet0 overload ip classless ip route 0.0.0.0 0.0.0.0 192.168.0.1 ip http server ip pim bidir-enable ! access-list 1 permit any no cdp run ! ! line con 0 line aux 0 line vty 0 4 login ! no scheduler allocate end

etiam#