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[king1]

something is mixed up here, you say you are sending the mail using you Outlook.com email address?

but the IP address 202.137.240.16 resolves back to NOW New Zealand Ltd. (AS9876) - my isp as it happens...

this tool below identifies the Ip address is associated with smtp.airnet.net.nz, which looks to belong to NowNZ, smtp is an outgoing mail server

https://mxtoolbox.com/SuperTool.aspx?act...n=toolpage

So it looks to Google like you are trying to send your Outlook.com email via the NOW NZ mail server smtp.airnet.net.nz
and the SPF is failing because the Outlook.com SPF record won't include a NOW NZ IP address.

I think I would be looking in you email settings in Outlook 2016 to see what incoming/outgoing mail servers are being used, for Outlook.com emails it would be smtp.office365.com

but clearly this is not the case, as identified in the gmail error, it looks like you could have that as smtp.airnet.net.nz