We've just moved to Office 365 as it's cheaper than our previous email provider. Email addresses all work for our users, now we need more control.

We need to send automated emails from our backend. We don't want to pay for a new user seat for each email address we might need to send as. How can we configure the Exchange server or Office 365 to allow us to do so?

  • You probably ought to consider using an outbound email provider like Amazon SES, Mailgun, etc. Office365 and their competitors are not meant for use cases such as yours.
    – EEAA
    Jan 22, 2015 at 18:48
  • @EEAA, thanks for the advice. If we were to use, say, Mailgun, what would we have to do on the Office 365 side to facilitate that? Or can we just send email through them claiming to be an email address at our domain?
    – Samson
    Jan 22, 2015 at 18:58
  • 1
    I run a linux box on prem that relays to the Office365 tenant, all internal back end mail is sent to the linux box and relayed from there.
    – Optichip
    Jan 22, 2015 at 19:05
  • @EEAA - What do you mean by "Office365 and their competitors are not meant for use cases such as yours."
    – john
    Jan 22, 2015 at 19:38
  • @john - Office365/GoogleApps/etc. are built for providing user email accounts, both inbound and outbound. Yes, you can shoehorn their products into providing outbound access to backend systems, but it's a hack, and is susceptible to being shut down for random reasons. Additionally, they typically have very restrictive outbound message limits. So - it can work, but it's not ideal. Using a purpose-built solution will be much less problematic in the long run.
    – EEAA
    Jan 22, 2015 at 19:41

2 Answers 2


The "From" and "Reply to" addresses, when sent via SMTP, can be literally anything you want them to, as long as you use SMTP authentication from your backend via a single account. I don't believe that O365 will let you configure anonymous relay.

Of course, to send email, you don't need to send through your O365 instance at all. You could just, you know, send the mail. Your backend applications could send mail directly, or you configure an SMTP relay on your network for your backend to use, and then that relay would just send the mail to the intended recipients.

Or as EEAA suggested, you can use a hosted email relay service.

  • So we could send email through a hosted service and say that it's from Impo[email protected]. Assuming we setup a distribution group with that address on Exchange replies to that email we sent would arrive as intended?
    – Samson
    Jan 22, 2015 at 19:15
  • Yes - you'll definitely want to do some reading up on SMTP and mail in general. Like I said, you don't even need to use a hosted service, your backend could be configured to handle directly sending mail or you could build a relay host or two in-house.
    – mfinni
    Jan 22, 2015 at 19:21

There's no requirement to use a specific FROM address when relaying email through O365 as a specific user. You only need a licensed account with a mailbox.

We've found benefits to relaying our mail though Office 365 which we didn't get from going direct to the receiving mail host:

  • You can make use of transport rules, outbound spam, malware filtering, etc.
  • If you've configured DNS as guided by Microsoft, you will have set up an SPF record. Annoyingly, (maybe sneakily) the guidelines instruct you to configure an SPF record that uses all 10 of your available SPF entries because of the recursive lookups.
  • If it's important to you, you can maintain a certain level of control over who/what is sending email. Just allowing any IP address to email out of your network is risky.

There is also the option to use an internal relay server, optionally with a TLS connection, into a receive connector in Office365. This gets you around the 10k/day recipient limit.

Here's the document you need to read: https://technet.microsoft.com/en-us/library/dn554323(v=exchg.150).aspx


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