Such is the nature of email now. Those who send spam try new (and old) tricks to land their messages in your inbox. Email servers and clients* beef up their spam detection to shield you from the annoying and especially harmful messages. Unfortunately, some junk messages slip through spam filters and some legitimate messages get false-positive flagged as spam.
What's wrong with the website?
Because the message arrived at your email client, even in the junk folder, the website and server likely did what they were supposed to do: they sent the message. What's more, you received the message—again, even though it landed in your junk folder. There are things we can try changing on the website but first, let's try handling the email messages at the delivery point.
What can we do about it?
Make sure you check your junk folder at least daily. Ideally, everything you find there can be swept away and forgotten. But you may find one or more messages that need your attention.
When you find a message from a trusted sender in your junk folder, first make sure it really is from that sender. For a message sent from a form on your website, it should come from an email address on your website domain. In some cases, where we send through a mail service, we may use a subdomain of your domain or a subdomain of ours. If unsure, ask.
Once you've confirmed the sender is safe, add the sender to your contacts. You also may have the option to mark the sender as "safe" or "trusted" for subsequent messages. Just what options you have available and how you access them will vary by email client. If a simple right-click on a message doesn't bring up one or both options mentioned, consult the client program's help content, or search Google or Bing.
So what else can we do on the website?
Depending on how we configured the form-fill handler to send, we may try changing the sender email address. There may be a safe-list somewhere between the website server and you that requires we follow a certain protocol or update a DNS entry for your domain. Don't worry about what this means unless or until we get to this point. If we manage your domain(s) for you, we'll handle this.
Another possibility, and one we would recommend, is to drop email notifications, altogether. If your team uses Slack, we can send inquiries and requests to one or more channels. If you use a customer support service like Zendesk, we could send the messages to create tickets. (At GSMG, we send inquiries from the form on our website to Zendesk, and then Zendesk sends messages to a Slack channel.) If you use an online CRM, we may be able to send contacts and their requests directly there. The point is, there are alternatives to email.
* The program you use to retrieve email from an email server is an email client.