What can cause a delay when sending an email notification about an order to an Opencart CMS user?

Question

opencart

Good afternoon!
There is such a problem.
If the order is successful, the email notification to the user comes with a delay of an hour, while the administrator receives it normally.
CMS Opencart 2.3
Maybe someone faced a similar problem?
I would be grateful for any help!

Answer 1

due to the exchange with the smtp server presumably