email smtp port 25 and 587 firewall rule/port forward protection

[RamSense]

humm… on Opnsense 21.7 I tried some different settings in the outbound rule.

When:
- changing the source to myVPN network address -> after some time, the iPhone 4g email stops working. It looks like it takes a couple of minutes before the changed outbound rule is taking effective.
- changing the source to the ip range of openvpn -> same result - stops working
- changing the source to <Lan address>  (I learned earlier that this is the opnsense ip-address on the lan only) -> same result, stops working
- changing the source to <Lan Network> same result
- changing to source to OpenVPN network -> same result - stops working
- changing to source to This Firewall -> I can receive emails on my MacBook Pro on local wifi and using an email to sent to my own email server e-mailaccount. Replying on that email back (with my own email server) is not working….
- changing to source any -> everything is working again…. I find this very strange… I should be able to narrow this rule in my opinion.

And when source is any -> on my iPhone 4 g -NOT connected to VPN - and trying to get email en sent email on the mail app for my own mailserver works also….

I surely do not know what is causing this all. I have on my synology firewall a rule to only accept port 587 and 993 to accept ip range lan and ip range vpn.
So when no vpn is on on the iPhone 4g, it should not accept email…. But it does… It looks to me that there is a flaw in opensense 21.7 to let the connection trough with the ip 192.168.1.1 (the ip of opnsense) ?

What is causing this? Openvpn fault? Opnsense 21.7 fault? Or my fault in what?