Do some or most universities allow retiring faculty to retain their faculty email accounts?

In my experience, most institutions do allow retired faculty to keep their email accounts.

The American Association of University Professors has issued a Statement of Principles on Academic Retirement and Insurance Plans which includes:

Each institution should help retired faculty members and administrators remain a part of the academic community, and facilitate timely retirement, by providing, where possible, such amenities as a mail address, library privileges, office space, faculty club membership, the institution’s publications, secretarial help, administration of grants, research facilities, faculty dining and parking privileges, and participation in convocations and academic processions.

Although "email account" isn't specifically mentioned on that list, it would seem to clearly be in the same spirit.

Of course, your institution has the power to make whatever policies they see fit.

As to your correspondence, I'd suggest asking whether it can be restored from a backup. They might be able to give you the data even if they won't mantain the account. Your department chair might be able to support you in this, particularly if your correspondence included other department business that may be relevant to current faculty.

Another request you could make is whether your institution could set up a forwarding address, so that when your correspondents send mail to [email protected], it gets forwarded on to your own personal email account. That saves the institution the trouble of having to maintain your account and store your mail, but you still get the benefit of being reachable through that address.

I have a friend who retired from Swarthmore who said "emeritus means forever" in response to my assumption that his e-mail would expire. Whether or not that's technically accurate, his e-mail persists.

Policy from Columbia: http://faculty-retirement.columbia.edu/post-retirement/faq-post-retirement#email%20address%20internet

Policy from Indiana: https://kb.iu.edu/d/dddx#email

I just retired from a private, liberal arts college. I may keep my e-mail account on the condition that I use it at least once each year, a pretty nominal requirement in my opinion.