Hey eherbert,
Thank for reaching out!
Sorry to hear you’re having issues with email deliverability. This is becoming a fairly common issue.
As spam is getting worse (and more clever), ISPs and email service providers are tightening their restrictions. What we’re seeing is they are starting to block and/or spam many emails that previously would have gone through and been delivered with no issues. This often includes WordPress emails.
When you send an email from Outlook.com, Gmail or similar service, that email is “verified” that it’s legit and did indeed come from that source.
By default, when your web server sends an email (which by proxy includes WordPress and WPForms), that email is NOT authenticated or verified. This is one of the metrics email providers are starting to leverage as they combat spam.
In short, emails that are not sent with an authenticated account or service have issues with deliverability. Sometimes they go through, other times they end up in the Spam folder or don’t get delivered at all.
The fix is to configure WordPress to send authenticated emails. We have an article that has more information about doing that, with links to several different methods (https://wpforms.com/send-emails-wordpress-using-smtp-step-step/#usinggmailsmtp). Our top two recommendations are:
1. Sending using SendGrid service (https://wpforms.com/fix-wordpress-email-notifications-with-sendgrid/) – SendGrid is a quick setup and be done in about 5-10 minutes. SendGrid is free to use for sending up to 12,000 emails each month which accommodates most users.
2. Sending using Gmail (or Google Apps) (https://wpforms.com/3-steps-to-use-gmail-to-send-wordpress-emails/)
Personally, I use SendGrid for all my own websites and projects. It takes about 5 minutes to setup and once it’s running it resolves any/all email delivery issues. That is definitely my recommendation.