And here’s the answer I’ve obtained:
Per discussion with our engineer, when use the calendar client over the calendar alias to contact it.
Our calendar will auto forward to non-alias to contact, this is the alias limitation.
But your question is only alias can use. We would like know did you have setting other web service or firewall block?
We suggest please use the other port or try use other customized port to use
Not only I don’t fully even understand what he’s saying (“auto forward to non-alias to contact”: what the hell does this means?) but I’m pretty sure they didn’t have fully understood the issue too (and I had given the URL of the current thread in the ticket details though).
So, even if I don’t like it, seem that I’m stuck to using the dedicated port instead of the alias.
I’m still fully convinced Synology devices and software are really great products but support is often abysmal.