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Exchange / sendmail

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Fred Martin_1
Valued Contributor

Exchange / sendmail

After years of using only sendmail and smtp/pop3 were are installing a MS Exchange server.

Almost everyone will still have a unix account for access to a database but won't be using sendmail. Exchange will be the primary.

Having said that, Exchange will be set up to relay email for the sendmail server, since system alerts and such will still be sent from there.

Additionally - I'd like to be able to maintain some email inboxes for certain employees, in sendmail.

We have warehouse staff and truck drivers that need email, but rarely, and don't need anything like the full MS Office suite.

I'm told that it's a pain to get Exchange to play nice with another server except Exchange.

I guess what I'm wondering is, can both Exchange and sendmail be mail servers for the same domain? Exchange being the primary, relaying email for sendmail and delivering mail to sendmail when it knows the recipients are homed there?

How would this be configured (roughly)?
Jose Mosquera
Honored Contributor

Re: Exchange / sendmail


If you can keep your current service Relay Server HP-UX sendmail could use it to dispatch outgoing emails.

Please check this recent post, I think that could be useful to start:


Honored Contributor

Re: Exchange / sendmail

Let's assume your email domain is "company.example" and one of the users you wish to keep using Sendmail currently has the email address Joe Trucker .

Both the Exchange and the sendmail servers need a proper DNS registration, although strictly speaking only the Exchange server really needs to see the DNS data of the sendmail server.

First, your Exchange server shall be the primary mail server, so in the DNS system, your domain's MX records should point to it:

company.example. IN MX 1

The Sendmail system should be configured with a different mail domain name altogether; perhaps "". To keep the spam filters happy, it would be good to create a MX record for it too, although it will be rather trivial one: IN MX 1

To allow the sendmail users to seamlessly send mail as before, you'll need to do two things:
1.) To make things simpler, you probably should configure sendmail on the unixmail system to use the Exchange server as its "smart host", through which all the outgoing mail is sent.

2.) You must configure sendmail at the "unixmail" system to _masquerade_ the sender domain as just "company.example" instead of "", so the sender addresses will be the same as before, and replies will automatically be directed to the Exchange server first.

(Note: it might be possible to do this address rewriting at the Exchange side too. I'm definitely not an Exchange wizard; basically ask your Exchange admin what kind of sender addresses the outgoing mail should have for Exchange to accept it for forwarding, and then configure sendmail to do it.)

3.) You must configure the Exchange server to enable the forwarding of outgoing mail sent from the "unixmail" system using "@company.example" sender addresses.

That covers the sending side.

For incoming mail, you should configure the sendmail users as mail aliases to Exchange, so that any mail addressed to e.g. jtrucker@company.example is forwarded to instead.

(It also might be necessary to specifically list in the Exchange configuration as a forwarding-enabled domain.)

When a mail recipient is a regular Exchange user, Exchange will simply deliver the message to the appropriate Exchange inbox. But when the recipient is aliased to, it should pass it on to the unixmail system, where sendmail should now recognize it as a message for a local user.

Fred Martin_1
Valued Contributor

Re: Exchange / sendmail

Matti, thank you. I'll keep this open for a bit.
Steven E. Protter
Exalted Contributor

Re: Exchange / sendmail


Exchange is designed to be the master of the mail universe, and will relay mail for Unix easily using the DS functionality of the sendmail daemon.

You can do this all on the GUI side of Exchange, so long as the sendmail daemon is running on those systems intended to accept inbound mail.

You can set up sub domains or alias mail boxes on the exchange server.

Exchange has a web based interface that will work with smart phones and similar devices, which may be an alternative to a PC and full suite as well.

Steven E Protter
Owner of ISN Corporation