The addressee does not receive mail, although it is listed as sent, what is the reason?

Question

gmail

On my site, people enter email and get results from it. Everything works fine, but the letter does not reach one person. In turn, in my mailing list, it is listed as sent to this addressee and there are no errors.
PS I sent mail to 20 different people, and the problem is only with one.

Answer 1

Go to spam. It is necessary to track the entire chain of transmission of the sent.