I have two accounts in Mail (v. 10.3), on a MacBook Air 13" running macOS 10.12.6. One is a work-related account with a POP configuration and the second one is from a hobby-group with an IMAP configuration. The work account has changed servers several times in the last few years. When the work account changed servers, I would add the new account, and leave the old inactive accounts on the mail app.
Today, I tried unsuccessfully to modify an existing account with the new servers addresses. I looked up analogous situations here and on other Mac forums to find out how to deal with my old accounts. I am worried that if I remove them completely, I will lose old emails.
Can I continue adding accounts with very similar information to old accounts without running into trouble? If not, how can I keep all my old messages under the most recent work account?