Multiple error messages like this in the application log:

• Failed to start listening (Error: 10049). Binding: [fe80::xxxx:xxxx:xxxx:xxxx%x]:25.
• Failed to start listening (Error: 10049). Binding: [fe80::xxxx:xxxx:xxxx:xxxx%x]:717.
• Failed to start listening (Error: 10049). Binding: [fe80::xxxx:xxxx:xxxx:xxxx%x]:465.

Ending with:

• Inbound direct trust authentication failed for certificate %1. The source IP address of the server that tried to authenticate to Microsoft Exchange is [%2]. Make sure EdgeSync is running properly.

The Microsoft Exchange FrontEndTransport service would not start. It was just restarting in an unending loop.

After checking the IPv6-address from the aforementioned events, I noticed that this address was not listed on my NIC any more. This address had changed!

Maybe this is a typical “school boy error”, and I should have done this a long time ago, but the solution to my problem was to remove Local IPv6-address from the Receive Connectors scope on said server. It is worth noting that I also re-established the Edge Subscriptions during this troubleshooting session, though this did not seem to fix anything. EdgeSync was working properly before, and after this error.

The transport service started.

Note to future self: Remove Link-Local IPv6 addresses from Receive Connectors on Exchange!