Open relay

Andy
Andy used Ask the Experts™
on
Hello,
I need to allow an external(cloud) app to send e-mail via on-premisse exchange server.
So,I need to configure open relay for two public IP addresses.
I checked those two IP address and they are Microsoft IP addresses.So,I presume it is Azure app.
Is it OK to allow open relay to public IPs like Microsoft?
If it is OK,I only need to add those two IPs on receive connector(anonymous) ?
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ste5anSenior Developer

Commented:
1) Yes. But is it sufficient? Not necessarily. Cause Cloud means also shared. Thus an evil attacker on the same Microsoft IP may than misuse your open relay.

Maybe you should look into Azure to on-premise VPN like Connect an on-premises network to Azure using a VPN gateway.
MichelangeloSystem Administrator / Postmaster

Commented:
Ciao,

Ms-Exch-SMTP-Accept-Any-Recipient – allows to relay email outside of your organization, as described in the article above.

Moreover, you may need to add:
Ms-Exch-SMTP-Accept-Any-Sender – You may want to bypass checks imposed on the sender address i.e. you may want to allow external senders. It may not be advised to set it but I list it for the dogmatic Sake Of Completeness

Ms-Exch-Bypass-Anti-Spam– Allows to bypass checks that may prevent delivery of emails when sent from malformed sender domains (useful for appliance reports and whatsnot)
Managing Consultant
Commented:
If you are already in Microsoft's cloud and need to send email, I recommend you take a look at Azure SendGrid. It's "free" for up to 25K emails a month.
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Author

Commented:


ste5anSenior Developer

Comment posted36m
1) Yes. But is it sufficient? Not necessarily. Cause Cloud means also shared. Thus an evil attacker on the same Microsoft IP may than misuse your open relay.

That what i am afraid of.

If you are already in Microsoft's cloud and need to send email, I recommend you take a look at Azure SendGrid. It's "free" for up to 25K emails a month.

Company is  not in the cloud but this app is in the cloud.So Azure SendGrid wont work?But company has test mailboxes on office 365(@onmicrosoftdomain)
Michael B. SmithManaging Consultant

Commented:
If they have test mailboxes in Office365 then they have access to the Azure portal and can set up SendGrid.

Author

Commented:
Michael,
Thank you for hint about sendgrid.
I will check this option.Never heard about sendgrid.
I will try to google it
So,company is on-premisse and has office 365 just for test and app is from another company in cloud.
If someone have advice how to configure send grid in this situation :-)
Thank you
Shaun VermaakTechnical Specialist
Awarded 2017
Distinguished Expert 2018

Commented:
I need to allow an external(cloud) app
Do you have control over it? Can you not use EWS?
Michael B. SmithManaging Consultant

Commented:
portal.azure.com and login using the global admin for the account

go to "all services"

enter "sendgrid" in the search box

click on the "sendgrid" result

on the following slab, click on "create sendgrid account"

follow the bouncing balls. :-)

Author

Commented:

Shaun VermaakTechnical Specialist/Developer

 
Do you have control over it?

I dont have control on this cloud app.

Author

Commented:
Michael,
thank you

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