We regularly have users flag the email they receive from this process as spam.
I have personally called to follow up in some cases to understand if our service was being abused or what the issue was. It was eye-opening. One user said "oh, yeah, I wanted that when I filled out the form but not when I got the email." Several marked the proposal as spam because they didn't like the final quote that was put together from their requirements.
Several said things like "I get too much email" and when pressed as to why they checked the box that said they wanted their quote delivered as an email replied that they didn't know, or they changed their minds, or they didn't want HTML email, or they didn't want a plain-text email, or their name was not in the subject line of the email, or that their company name was not in the subject line of the email.
This is a very low volume, very expensive, highly technical product. We're talking maybe a dozen requests per day nationwide. So those people flagging the emails as spam have a significant impact on the overall deliverability to services like GMail.