Unable to Establish StartTLS Connection

[Richard_Steiner]

Hello,

I have just installed on-premise exchange server and configured hybrid with office365. However, I noticed that I am not able to establish a StartTLS connection with office365 on port 25 and this causes email from on-premise user to a cloud user to fail. I have allowed all services on the firewall policy just to be sure that I am not blocking it but it still fails. I have attached a screenshot of failed connection test form behind fortigate and successful test from outside of Fortigate.

I am a self taught administrator on Fortigate FW and appreciate all the support I can get.

Cheers,

~Richard

[pminarik]

Make sure to run the test through a firewall policy without UTM inspection. To rule out interference from that. Otherwise I'd suggest doing a packet capture of both sides, then check if the replies coming in on WAN differ from what the client sees. It's still plaintext, so it should be easy to read.