Can mail be blocked when sending from a form on the site?

Question

Email

There is a simple landing page (test questionnaire, lead generator), on it is a form with an email to receive an answer. Sending emails via Swiftmailer. Then someone whispered to the customer (without arguments) that they would block the mail or go to spam if a lot of letters start leaving, and if the mailers are not real, then curse on the holder. There is no distribution. One form - one letter.
In what case can mailers block the mail from which the application leaves (the answer in my case)?

Answer 1

If spam is received from your feedback form, your server's outgoing submissions may be blocked. Make a captcha or check for links in the php code.
PS Most often, spam looks like text and a bunch of links.