Every year I've done an e-file tax return, I've used a digital signature. It's definitely a question for legal, though, as the laws and policies governing what is acceptable for digital signatures is going to heavily influence implementation.
You're also setting yourself up to manage PII, so please let me be the first to welcome you to the wonderful world of HIPAA.
"There are three kinds of lies: lies, damned lies and statistics."
- Benjamin Disraeli
First for "local" traffic if the adapters are in different networks with unique address ranges then the decision is based on the target IP address as to which network to use, logical really.
For external addresses not within any of the networks it will tend to be in order of metrics, for some reason the last network added (say you plug in a cable whilst you are on wifi) seems to get pushed to top priority which may be decided on the speed and stability of the cabled network and that it can see the internet or might just be cabled is better than wifi.
To set individual metrics; Open Adapter Properties, double-click IPv4 protocol and click the Advanced button bottom right, there you can set the metrics for IPv4 on that adapter, untick Automatic Metrics and set the adapter you want to be high priority to the lowest value and all the other adapters to higher numbers in order you want them to be searched.
Caveat is that Win 10 ignores this and no matter how you try sets it back to automatic, think it is an open issue at MS.
With ForceBindIP you can bind any Windows application to a specific interface or IP address. It´s freeware"
"ForceBindIP works in two stages - the loader, ForceBindIP.exe will load the target application in a suspended state. It will then inject a DLL (BindIP.dll) which loads WS2_32.DLL into memory and intercepts the bind(), connect(), sendto(), WSAConnect() and WSASendTo() functions, redirecting them to code in the DLL which verifies which interface they will be bound to and if not the one specified, (re)binds the socket. "
I tried switching off IPV6 but it didnt work it shows "DNS request timed out timeout was 2 seconds" almost every time these is the DNS communication as captured by wireshark when I type 'nslookup' and open the program
5 4.080346 192.168.1.6 192.168.1.1 DNS 84 Standard query 0x0001 PTR 18.104.22.168.in-addr.arpa
6 4.336621 192.168.1.1 192.168.1.6 DNS 113 Standard query response 0x0001 PTR 22.214.171.124.in-addr.arpa PTR D-Link.DSL2740B
and when I type 'facebook.com'
21 12.931466 192.168.1.6 192.168.1.1 DNS 81 Standard query 0x0002 A facebook.com.DSL2740B
22 12.965884 192.168.1.1 192.168.1.6 DNS 156 Standard query response 0x0002 No such name A facebook.com.DSL2740B SOA a.root-servers.net
23 12.966017 192.168.1.6 192.168.1.1 DNS 81 Standard query 0x0003 AAAA facebook.com.DSL2740B
29 14.976087 192.168.1.6 192.168.1.1 DNS 72 Standard query 0x0004 A facebook.com
30 14.980174 192.168.1.1 192.168.1.6 DNS 88 Standard query response 0x0004 A facebook.com A 126.96.36.199
(first field is the packet number,second:time,third:source IP fourth:dest IP fifth:protocol sixth:length seventh:description) why is my gateway's name appended on facebook.com (facebook.com.DSL2740B) when I type set type=mx or set type=all the MX and ANY queries are sent and there is no reply any help ??