Outgoing mailserver to compliment 0365

[JRoe]

We have an issue where our migration to o365 has created some issues, which I believe an on-prem HMailserver will fix. We have a trigger that will generate about 1000 email messages. There is no way around it in our system to stop or change this, and none of our partners have the resources to change the way this works. We switched from on-prem exchange to O365 and hit the 'you can't send any more email to this client..' issue. So, we engaged with a cloud SMTP provider, which worked.. until a change has us sending 50Meg mail attachments and it's killing our plan.

Our MSP thought putting on on-prem exchange server would work.. but since it ties into o365 we hit the limits again.

My thinking is let's just install hmailserver as an SMTP server on-prem, and have it send out the email to our partners. I don't need it to accept any inbound mail, and messages that bounce could be forwarded over to our 365 mailboxes, as the email address for those wouldn't be hosted on the machine.

Set it up with an internal domain, that has 1 mailbox, and open it up to our processing machines IPs, to let it accept messages, and it in turn will send them out..

Before I go down the path, just wanted to see if others were doing this or if there is some glaring faults in my logic.

[johang]

if you want to setup an smtp-relay/ smtp-out ( an email server that sends out email ) it does not need to accept incoming email, it should be externally recognised with use of spf, dmarc and dkim. The problem is getting a good reputation so the BIG ( gmail, outllook ) email providers will accept email from that host.

you are reffering to an internal domain, i would us a subdomain