Cisco ASA 5505 SMTP Problems

Hello,

I recently configured a Cisco ASA 5505 for one of my clients.
 Everything works on the network EXCEPT inbound Email, even though I believe I have SMTP properly forwarded to the Exchange server. Some Emails are coming in at a trickle while others are not coming in at all. They're using appriver spam filtering and when I called appriver support, they confirmed that the ASA is killing SMTP connections almost as soon as they are opened and they had a backlog of Emails waiting to be delivered.
 I read somewhere that ESMTP filtering on the ASA could be the cause of the problem and I have disabled it. I won't be able to test if this fixed it or not until tonight when I go back to the client again and place the ASA back into service. Can anyone think of any other reason why this issue may be occurring? Thanks!
Here's my running config:

: Saved
:
ASA Version 7.2(2)
!
hostname mcASA
domain-name *********
enable password encrypted
names
!
interface Vlan1
 nameif inside
 security-level 100
 ip address 192.168.1.1 255.255.255.0
!
interface Vlan2
 nameif outside
 security-level 0
 ip address ***.***.**.** 255.255.255.248
!
interface Ethernet0/0
 switchport access vlan 2
!
interface Ethernet0/1
!
interface Ethernet0/2
!
interface Ethernet0/3
!
interface Ethernet0/4
!
interface Ethernet0/5
!
interface Ethernet0/6
!
interface Ethernet0/7
!
passwd encrypted
ftp mode passive
dns server-group DefaultDNS
 domain-name ********.***
access-list inbound extended permit tcp any any eq 3389
access-list inbound extended permit tcp any any eq ssh
access-list inbound extended permit tcp any any eq smtp
access-list inbound extended permit tcp any any eq https
access-list inbound extended permit tcp any any eq www
access-list inbound extended permit icmp any any
pager lines 24
logging enable
logging asdm informational
mtu inside 1500
mtu outside 1500
icmp unreachable rate-limit 1 burst-size 1
asdm image disk0:/asdm-522.bin
no asdm history enable
arp timeout 14400
global (outside) 1 interface
nat (inside) 1 0.0.0.0 0.0.0.0
static (inside,outside) tcp interface 3389 192.168.1.103 3389 netmask 255.255.255.255
static (inside,outside) tcp interface ssh 192.168.1.11 ssh netmask 255.255.255.255
static (inside,outside) tcp interface smtp 192.168.1.103 smtp netmask 255.255.255.255
static (inside,outside) tcp interface https 192.168.1.103 https netmask 255.255.255.255
access-group inbound in interface outside
route outside 0.0.0.0 0.0.0.0 ***.***.**.** 1
timeout xlate 3:00:00
timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 icmp 0:00:02
timeout sunrpc 0:10:00 h323 0:05:00 h225 1:00:00 mgcp 0:05:00 mgcp-pat 0:05:00
timeout sip 0:30:00 sip_media 0:02:00 sip-invite 0:03:00 sip-disconnect 0:02:00
timeout uauth 0:05:00 absolute
username **** password ******* encrypted
http server enable
http 192.168.1.0 255.255.255.0 inside
no snmp-server location
no snmp-server contact
snmp-server enable traps snmp authentication linkup linkdown coldstart
telnet timeout 5
ssh 192.168.1.0 255.255.255.0 inside
ssh timeout 5
console timeout 0
dhcpd auto_config outside
!
dhcpd address 192.168.1.2-192.168.1.129 inside
!

!
class-map inspection_default
 match default-inspection-traffic
!
!
policy-map type inspect dns preset_dns_map
 parameters
  message-length maximum 512
policy-map global_policy
 class inspection_default
  inspect dns preset_dns_map
  inspect ftp
  inspect h323 h225
  inspect h323 ras
  inspect rsh
  inspect rtsp
  inspect sqlnet
  inspect skinny
  inspect sunrpc
  inspect xdmcp
  inspect sip
  inspect netbios
  inspect tftp
!
service-policy global_policy global
prompt hostname context
Cryptochecksum:79f3ff1db6fe1ea5d5a149971605fc5f
: end
asdm image disk0:/asdm-522.bin
no asdm history enable