[horde] tie_to vs. alias addresses

[Steffen]

What is the difference between the tie_to and alias addresses?

The only hint I' ve found so far is that tie_to is used to select an
identity from an email address. Is this the only usage?
When are alias addresses used?

Is there a (developer) documentation describing when to use which
preference?

I tested that I can place the _same_ mail address into both tie_to and
alias address of two identities of the same account. There is no check
for uniqueness. Also, those addresses are not verified, like the from
address is.

-- 
Steffen