Sending emails using python SMTP from gmail to outlook being blocked

I am trying to send emails from my domains mailbox which is google based but it is being blocked with the following error: 

450 4.7.26 Service does not accept messages sent over IPv6 [2607:f8b0:4864:20::f2e] unless they pass either SPF or DKIM validation (signature failure).

Emails being sent to outlook if they are received are frequently ending up in the junk folder. I have a paid service so all users receiving emails from my platform are expecting these emails and I'm almost only having this issue with outlook, is there anything i can do from my end so that outlook stops flagging my emails to my customers?