Cloudflare Tunnels

I would be extremely surprised if there was one, as there are about 70000 banks in the US.

Some of the large banks now have APIs to access their data, but those aren't publicly available.

Most smaller banks and credit unions don't have a public API, so apps like Mint rely on web scraping. That's a huge and expensive undertaking, considering that web sites change constantly and all the scraping could has to be adjusted for it.

Companies like Intuit are willing to invest the time it takes to keep up because they can sell your data (I guess) or sell you additional products. I don't see how the open source community could keep up with this.

I haven't tried it myself, but SRS (Sender Rewriting Scheme) might work for your use case. It is designed to route bounces back through a chain of email servers and is specifically supposed to solve your forwarding scenario. There's PostSRSd that can add this capability to Postfix.

Otherwise you really need a SMTP relay that is not focused on transactional emails, but I'm not aware of any free ones (for obvious reasons). Services like pobox.com or mxroute.com might be usable as SMTP relays, but they obviously have a cost, which might not be worth it.

I was in the same situation and eventually caved in and just routed all my personal email and domains to Fastmail, and only use smtp2go for transactional emails sent by my servers.