Very strange problem, my guess is a configuration error. Clients connecting to an 1841 with a VPN tunnel endpoint on its Dialer0 interface (ADSL WIC on an ISDN line) have no trouble accessing LAN resources (file shares, Exchange mailboxes via a MAPI client, ping, etc.). However, when configuring an IMAP connection on a remote VPN client, outgoing email would not send. The strange thing is that the port 143 traffic between the client and IMAP server flows properly.
It turns out that port 25 traffic correctly flows from the client to the SMTP server, but that return traffic from the server to the client does not flow back through the VPN tunnel. Instead it routes back out through the public IP address. Can anyone offer a suggestion? (And please feel free to comment on the config in general, i.e. unnecessary ACL entries, etc.)
The VPN address pool is 10.10.10.0/24. The LAN subnet is 10.0.0.0/24. Host 10.0.0.209 is the SMTP server. xxx.xxx.xxx.xxx is the public IP address on Dialer0. The packet trace follows and the config is attached as config.1821.cisco.forum.txt.
<snort trace>
12/16-07:14:47.757578 10.10.10.17:3753 -> 10.0.0.209:25
TCP TTL:128 TOS:0x0 ID:10758 IpLen:20 DgmLen:48 DF
******S* Seq: 0x65389798 Ack: 0x0 Win: 0x8000 TcpLen: 28
TCP Options (4) => MSS: 1260 NOP NOP SackOK
=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
12/16-07:14:47.845437 xxx.xxx.xxx.xxx:25 -> 10.10.10.17:3753
TCP TTL:127 TOS:0x0 ID:23397 IpLen:20 DgmLen:48 DF
***A**S* Seq: 0x4AE8EFC0 Ack: 0x65389799 Win: 0x44E8 TcpLen: 28
TCP Options (4) => MSS: 1452 NOP NOP SackOK
=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
</snort trace>
