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Inbound OnPremises connector seeing significant mail flow without TLS warning
We have Office 365 email licenses and we use MS Office/Outlook 2019 on Microsoft Windows Servers v2019. We do NOT have an OnPrem email server. We used to use smtp.office365.com as an smtp server...
- If the ERP app doesnt support TLS1.2 then no matter where you send it won't be capable of TLS1.2. The connector would pick up the traffic as it's coming from your on-premises public IP, regardless of if you use smtp.office365.com or the MX record.
Set up an IIS relay on prem, use that as your relay and send from there securely to Exchange Online
I have this issue either coming from on premise Exchange or on premise SMTP relay server. My problem is that I think I will need to split this traffic into separate connectors to figure out what server is sending without TLS. Just FYI, when I had a ticket open for issues with relaying email from on premise I was told that using an on Premise IIS/SMTP replay is not a supported configuration. Since IIS/SMTP relay is an IIS 6.0 protocol that it is no longer supported. You may need to think about looking for a different solution.