How often to update information about mail servers?

Question

Email

I am engaged in sending out mail messages (according to my database, not spam, even Yandex thinks so :) )
With each mailing, I run the entire list through several filters, the first of which checks whether there is such a mail domain (mx) and whether it is valid.
Obviously, most of this list is unchanged, mail domains are usually paid for a year or more, so it makes no sense to check the existence of somefirm.ru once a day, and some domains are almost eternal (any mail.ru and yandex, for example)
The question is how often it is necessary to check the domain for correctness? You can, of course, create a white list that is not checked, but it seems wrong to me to fill it in manually.

Answer 1

So why check domains before mailing? Problems can be temporary / one-time, for example, they forgot to renew the domain on time. Configure the maximum delivery time in the MTA, catch callbacks from the mail server (for this, it is advisable for each recipient to form a separate letter from a unique sender address in the envelope-from). If you received, for example, 3 hits on the latest mailings, remove the user from the list. Boxes can "die" even on live domains.

Answer 2

not spam, even Yandex thinks so

Article 18.1
Distribution of advertising over telecommunication networks, including through the use of telephone, facsimile, mobile radiotelephone communications, is allowed only with the prior consent of the subscriber or addressee to receive advertising. At the same time, advertising is recognized as distributed without the prior consent of the subscriber or addressee, unless the advertising distributor proves that such consent has been obtained.