with V8.7 sendmail, addresses with and without a
host part that resolve to local delivery are handled in the same way.
For example, user and
email@example.com are both looked up with the User
Database (userdb) and processed by the
localaddr rule set 5 (Section 19.6). This processing can result in those
addresses being forwarded to other machines.
With the stickyhost feature, you can change this
By defining stickyhost, you are telling
sendmail to mark addresses that have a local
host part as "sticky":
user not sticky
Sticky hosts tend to be delivered on the local machine. That is, they
are not looked up with the User Database and are not processed by the
localaddr rule set 5.
One use for this feature is to create a domainwide namespace. In it,
all addresses without a host part will be forwarded to a central mail
server. Those with a local host part will remain on the local machine
and be delivered in the usual local way.
Note that this is opposite the behavior of the former
notsticky feature of V8.6.