Recent members often ask me to delete old accounts, such as those created two, three or four years ago.
So I explain my point of view which is the following. Personally, I feel that an account is really dead only when it has become unreachable. So, in my opinion, even if the member does not connect for a few years, as long as his email answers, he remains a potential member, he is just asleep.
The experience shows me everyday that old accounts suddenly wake up and remember the site, probably because they received a few notifications at the right time. There are many reasons that can cause a longer or shorter, but often temporary, abscence.
So I stubbornly refuse to rely solely on the date of creation of the account or the date of last connection.
However, every week, I delete all accounts with an email address that returns an error, (bounced) either because it is full, so probably abbandonne, or because it no longer exists, then in this case, the member is definitively lost.
In this way, I can assure other members that each member is reachable. Of course this method is probably not valid for all types of site.
In general, this method shows me that an email box lasts about 6 years, rare are the accounts that survive beyond.
So, for me it is very important to have an SMTP service that allows me to follow the emails correctly.
Below, statistics on the last 30 days. You can see that the notifications are largely delivered, especially as in the part that is not, there is a large part of fake profiles that use emails that do not work, and that do not confirm their account.
And you clean up the accounts and on what criteria?