503 Service Unavailable error


1 week ago i‘ve setup an opnsense firewall with haproxy and letsencrypt. i did the setup exactly as described here: Klick

Instead of many different vlans i only use 1 subnet:
And instead of an nextcloud Server i use an exchange server. Server ip
Also i dont use the proxy server and url filter.

I can connect from the outside and also from the inside to the Exchange Server, so this seems to be working. My Problem now is that on the exchange Server i cannot reach out to other Websites, for example www.google.at, i always get an certificate error, also when i want to open a website with port 80 (downloading the letsencrypt certificate crl) i get 503 service unavailable error.
I can resolve the dns of google so that is working.

Can you please help me fixing this issue?