Email with a link to file
I have a form which is sending an email. I'd like to add to the email a link to a file. The email is not send if the link contains https://s18718.pcdn.co/wp-content/
https://domain.com/wp-content/uploads/2018/03/my.pdf email not send
https://domain.com/uploads/2018/03/my.pdf email send
Is it a normal behavior? Any turn around?