I have over 200 sites on the Managed WordPress Platform - generally I do not have issues with emails going to spam, however occasionally I will come across one site (even on a VPS) due to the domain settings that do.
In cases like this I use AWS Simple Email Service (SES) it's $0.10/1000 emails sent - And there is a free WordPress plugin called WP Offload SES Lite
The biggest thing I needed to do was authenticate either the domain or the email which WordPress was send the emails as. That solved my problem in "30 seconds" once the AWS account was setup and out of sandbox mode.
I will also share that I have not found a specific "this setup with this provider" causes the issue it's just happen stance
Check out my site! | I currently manage over 300 WordPress Websites
* Please note that I offer free advice on this forum. Thank You Info If you would like personalized help, please contact me. Otherwise, please ask your question in the proper forum so the answer can assist EVERYONE in the community and not just you. Thanks! *
Once your issue is resolved,
please be sure to come back and click accept for the solution