Long FTP+POP3 server response, what is the reason?

Question

Computer networks

Good afternoon connoisseurs. There are VPS. The sites work flawlessly. However, when entering through the FTP manager to the server, there is a delay of 3-5 seconds. Same thing with receiving/sending mail via MS Outlook. Other hosts don't have this problem. From another IP, everything also works instantly. What could be the problem?

Answer 1

logs, tcpdump, wireshark
someone is waiting for a certificate, most likely, but maybe a route