Hi, This sounds like an SMTP issue not IFS Connect related.

I checked online and found this troubleshooting notes:

URL - https://docs.microsoft.com/en-us/Exchange/mail-flow-best-practices/fix-issues-with-printers-scanners-and-lob-applications-that-send-email-using-off?redirectSourcePath=%252farticle%252fFix-issues-with-printers-scanners-and-LOB-applications-that-send-email-using-Office-365-c75542a8-c792-42c0-a8c5-291df987512d#TroubleshootSMTP

1. 5.7.60 SMTP; Client does not have permissions to send as this sender.

   For example, if you entered login credentials for sales@contoso.com in your application settings, but the application tries to send emails from salesperson1@contoso.com, this is not supported. For this scenario, use Office 365 SMTP relay instead.

2. Test the user name and password by logging on to Outlook on the web, and try to send a test email to make sure the account is not blocked. If the user is blocked, you can find help in the article, Removing a user, domain, or IP address from a block list after sending spam email.

3. Next, test that you can connect to Office 365 from your network by doing the following:

4. Follow the instructions to install the Telnet Client tool on a computer on the same network as the device or application.

5. Run the tool from the command line by typing telnet.

6. Type open smtp.office365.com 587 (or substitute 25 for 587 if you are using that port setting instead).

7. If you connected successfully to an Office 365 server, expect to receive a response line similar to this:

   220 BY1PR10CA0041.outlook.office365.com Microsoft ESMTP MAIL Service ready at Mon, 1 Jun 2015 12:00:00 +0000

8. If you can't connect to Office 365, your network firewall or Internet Service Provider (ISP) might have blocked port 587 or 25. Correct this so you can send email from your printer.

9. If none of these issues applies to your device, it might not meet requirements for Transport Layer Security (TLS) encryption. Your device must support TLS version 1.0 or above. Update the firmware on the device to solve this, or try one of the other configuration options where TLS is optional.

   For more information about TLS, see How Exchange Online uses TLS to secure email connections in Office 365 and for detailed technical information about how Exchange Online uses TLS with cipher suite ordering, see Enhancing mail flow security for Exchange Online.

Hope this helps.