configuring mx record for alternate delivery location

my company used microsoft hosted exchange services (bpos for short)

my mx record is pointing to microsoft

i have an internal server setup to receive mail
the same domain that my microsoft hosted exchange services uses

can i setup a second mx record SO if the user is not found on my hosted exchanged environment, it will try to deliver to the alternate location?

im using an app internally which generates email accounts for receiving messages.  these accounts are never setup in microsoft hosted exhange, so when i email these accounts microsoft sends a NDR that the recipients email address does not exist.

is it possible to correct this with additional mx records?
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Neil RussellConnect With a Mentor Technical Development LeadCommented:
In exchange you can set a setting entitled....  "Forward all mail with unresolved rcpts to this host"  found in the smtp server settings (depends on exchange version) And then you specify an alternate SMTO server.

Now as to if Microsoft shared hosting supports this I do not know but exchange does. Speak and ask them. THey would just need the IP of your other SMTP Mail server to forward unresolved emails to.

Neil RussellTechnical Development LeadCommented:
The MX points to any valid Mail server for your domain. If the server on the end of it is valid for your domain and returns a USER NOT KNOWN error to a sending smtp server than that server assumes that it is an authorative answer.
Neil RussellTechnical Development LeadCommented:
WHat server do you have setup internally? You could set your MX to to your server and then configure it to forward on all unknown mail directly to the server pointed to by your current MX record.
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sknoll84Author Commented:
its a third party product, ecm solution which runs its own mail server
this server is externally accessible

are you saying i may possibly be able to have my hosted exchange forward unknown mail to the second mx record?  or does it involve a different process?  i can call microsoft to check, i just want to be clear first

thanks for your help
If you have one mx pointing to microsoft and one mx pointing to your server, then all mail will typically be tried to deliver to the "better" one (lower priority value). In case of e.g. connection failure the mx with worse priority should be tried next, but not in case of a permanent error (such as USER NOT KNOWN).
In theory, if you could coerce your server to respond with a different (non-permanent) error message instead, things *might* work out, i.e. senders might try the microsoft server instead. (Note that this woul d not be RFC compliant, so don't do it anyway).
However, in case of congestion etc. that server might be tried anyway even for existing users.
sknoll84Author Commented:
very good explanation hagman

so it sounds like this simply isnt going to work
Neil RussellTechnical Development LeadCommented:
Its exactly the same explination as I gave you in the first post with a few extra words thrown in :D
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