Keep in mind we are talking about two different access-lists. The first one is the inbound access-list on the outside interface. This is the one that the sysopt permit-ipsec command allows IPSec traffic to bypass. If you do not do this then you will need to ensure that any IPSec initiator on the outside is added to that ACL or they would never be able to initiate an IPSec session.
The next ACL is the interesting traffic ACL. This is the one that says? If this traffic matches this ACL then encrypt it (or decrypt ? depending on which direction it?s going).
This is the ACL that you would put your limits on what servers and services the connecting clients can connect to. If you only want them to access your mail server vial SMTP then create your interesting traffic ACL such that only the mail server can talk to the clients via SMTP (the ACL will get mirrored on the remote side so you?re only creating the half that allows outbound traffic).Of course if you have more servers and services you can add them in.
This ACL usually reads permit IP any any for ease of setting up the IPSec tunnel and for site-to-site VPN?s that is usually what you want. But there is no reason you can?t use this ACL to lock down to be more specific.
Use vpn-filter command in the Group-policy level.