ASA 5505 using 1 Static IP disallowing PAT mapping for SMTP

I have been playing with an SMTP problem for days.  My problem is that I can't get the PAT to work with SMTP.  I am using a single static IP address, an ASA5505, and have tried static mappings [static (inside,outside) tcp 10.10.10.10 smtp 192.168.50.2 smtp netmask 255.255.255.255] and ACLs (as you can partially see below), but nothing has worked to this point.  I may have a DNS problem (not sure what I need in the MX record/DNS entry out with internet DNS servers), but I have tried inputing about everything there, as well, with little in the way of results.  (I currently have a basic A record pointing to default.domain, which is my actual domain name, with an MX record pointing to email.default.domain, which I had statically mapped in my ASA to an internal IP address).  

Please, someone help, as I cannot get my Small Business Server 2003 Exchange Services to accept inbound messages.  Outbound works fine, but inbound I get no Undeliverable or otherwise messages on the sending end.  It just dies in the ASA.  Packet traces also get killed either with a message that reverse-path-verify fails or that it is denied by the implicit rules (depending on which configuration I was running at the time).

Below is my config.  It is incomplete at this point, as I have tried about 20 different fixes I've found on the net with little in the way of results.  The 10.10.10.10 address is my static public IP and the 192 are my internal addresses.  I have removed the static email.default.domain entry at this point, as well, through my testing.  Otherwise, it was a name pointing to 192.168.50.2 with an entry of email.default.domain.  There is then a cname entry on that server, which is running DNS,with the proper FQDN of email.default.domain.

A possible gotcha in the future, but not sure if it's contributing to this problem, is that I have mapped the proper DNS entry with my Domain provider, but my ISP still has a record that's associated with the IP that I was given.  For example, I assigned 10.10.10.10 with default.domain with the company I bought the domain name from, and you get the proper NSLOOKUP when you perform it against the domain from anywhere ont he Internet, but a reverse lookup gives you the DNS entry associated originally with the ISP's IP address (something like "tx-10-10-10-10.sta.ISPhsd.net").  Could be contributing to the problem, but maybe not.

PLEASE HELP!

ASA Version 7.2(2)
!
hostname <hostname>
domain-name default.domain
enable password XXXXXXXXXXXX encrypted
names
!
interface Vlan1
 nameif inside
 security-level 100
 ip address 192.168.50.1 255.255.255.0
!
interface Vlan2
 nameif outside
 security-level 0
 ip address 10.10.10.10 255.255.255.224
!
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 XXXXXXXXXXXXXXXXX encrypted
ftp mode passive
dns domain-lookup inside
dns server-group DefaultDNS
 name-server 192.168.50.2
 domain-name default.domain
same-security-traffic permit intra-interface
object-group network Server
 description Domain Controller/Email Server
 network-object host 192.168.50.2
access-list inbound extended permit tcp any host 10.10.10.10 eq smtp
access-list outside_access_in extended permit tcp interface outside eq smtp object-group Server eq smtp
access-list inside_access_out extended permit tcp interface outside eq smtp object-group Server eq smtp
pager lines 24
logging enable
logging timestamp
logging buffer-size 16000
logging buffered debugging
logging asdm informational
mtu inside 1500
mtu outside 1500
ip verify reverse-path interface inside
ip verify reverse-path interface outside
ip audit info action alarm drop
ip audit attack action alarm drop
icmp unreachable rate-limit 1 burst-size 1
asdm image disk0:/asdm-522.bin
no asdm history enable
arp timeout 14400
nat-control
global (outside) 1 interface
nat (inside) 1 0.0.0.0 0.0.0.0
access-group inside_access_out out interface inside
access-group outside_access_in in interface outside
route outside 0.0.0.0 0.0.0.0 10.10.10.2 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
http server enable
http 192.168.50.0 255.255.255.0 inside
no snmp-server location
no snmp-server contact
snmp-server enable traps snmp authentication linkup linkdown coldstart
telnet timeout 5
ssh timeout 5
console timeout 0
dhcp-client update dns server both
dhcpd update dns both override interface inside
!
dhcprelay server 192.168.50.2 inside
dhcprelay timeout 45

!
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 esmtp
  inspect sqlnet
  inspect skinny
  inspect sunrpc
  inspect xdmcp
  inspect sip
  inspect netbios
  inspect tftp
!
service-policy global_policy global
prompt hostname context
Cryptochecksum:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
: end

Thank you in advance for your assistance.  Everything I have seen out there tells me that one IP will work fine for a small business if I setup the PAT correctly, but nothing has worked to this point.

-NickStart Free Trial