I have used my customer's email as From address for email notification in a contact form, and the E-mails are sent through/Via Sendgrid, but they are ending up in spam/junk folder.
Is there any workaround to stop the emails ending up in spam.
Twilio SendGrid developer evangelist here.
Sending emails from an email address that you don't own is an excellent way to end up in the spam folder.
Instead, you should send the email from a domain that you own. You can prove that you own the domain by going through the domain authentication process.
Once you have authenticated the domain, you can then send emails from any email address on that domain. Since this is a contact form, you want to reply to the person that entered their email address. You can do this by setting a Reply-To header with that email address. This will mean that the email will send from your own domain, but when you click reply in an email client you will reply directly to the person's email.