Selecting a send connector

A single organization can contain multiple send connectors, so Exchange has to decide
which one to use when sending an outbound message. Here’s what Exchange does to
select a send connector:
1. Gathers a list of all available send connectors.
2. Discards any disabled connectors or any connectors that are down.
3. Discards all connectors that have a maximum message size less than the size of the
message.   
4. Selects connectors that are available (in scope) for the originating server and whose
address space accommodates the recipient’s domain. (An address space of * matches
all domains.)
5. Selects the connector that has the closest address space match. For example, if one
connector has an address space of * and another has an address space of fabrikam.
com, any messages addressed to the fabrikam.com domain will be routed to the
second connector.
6. If more than one available connector exists, determines the best choice by the
following:
a. Least routing cost based on aggregated site costs. A connector in the local site
will always be preferred over a connector hosted in a remote site.
b. Whether the connector is hosted by the same Mailbox server that is making
the routing decision. A connector on the same server is always preferred over a
connector on another hub transport server on the same site.
c. Alphanumerically, meaning that the connector name that comes first in
alphanumeric order is used.
Hopefully, your messaging environment is organized in such a way that Exchange never
has to resort to alphanumeric selection from a range of connectors hosted by servers in the
local site!