Mail.ru throws out letters that contain the word "link". How to send emails from a third-party smtp server without getting into spam?

Question

SMTP

I have a site. And to send registration emails, I use the SparkPost email delivery service . When registering on my site via mail, the user does not receive a letter if the body contains the word "link". i.e. "Please verify your account using the link: http://". At the same time, it doesn’t even get into the spam folder, just mailru throws out the letter. How to make sure that all letters reach the addressee? Or are there alternatives for SparkPost