Fix an error on the site related to sending smtp mail

Hello, dear experts!

Our site (an online store created in yii2) from the afternoon stopped sending postal letters with order details (order composition, type and delivery details, etc.). At the same time, at the time of ordering, the site gives an error, but the order remains in the database.
For sending, smtp.mail.ru was usually used, they tried smtp.yandex.ru - to no avail.

you must resend emails to clients by using smtp

Unfortunately, the organization that designed our site has long ceased to exist, so we will be grateful for the solution of our problem!