@loughconn 

Hi, Thank you very much for the feedback.

Have you created any parental control profiles and added some content filters?

Did it help if we tried to disable the "Malicious Content Filter" under Network Security?

By the way, I noticed you had the Deco for a while. Did this issue just start recently?

Best regards

  @loughconn 

Hi. please also change the ipv4 DNS server to 8.8.8.8/8.8.4.4-How to change DNS server settings on my Deco

Would there be any error message when Outlook/Teams failed to work?

Was there an ISP router/hub installed in front of the Deco M9 Plus?

- If yes,  you could try to set Deco into Access Point mode to see whether it helped:

How to set up Deco to work in Access Point mode

Moreover, I saw some users mentioned the inappropriate MTU size might cause the current issue. Deco M5-1.7.8 supports modifying the MTU size(M9 plus doesn't yet).

When you are available, you could set Deco M5 as the main Deco and set the MTU size to 1492 or you could find the proper MTU size per FAQ-How to find the proper MTU size for my network

Thank you very much and best regards.