I have a couple of yahoo accounts which are essential to my life, especially the archives which go back with years of important work-related correspondence. Now I keep getting messages from Yahoo about something or other I need to do in order to continue using my Mail program on Mac so that my email continues to work. (I’ve quoted it below.)
My ex, who was always the household computer genius, tells me that if I go through the steps wrong I may lose ALL MY ARCHIVED EMAILS. Is this really possible?
I have until October 20 to sort this out, and my fallback position is that I’m just going to go to our local Mac store where they will cheerfully take care of this for me for $30. But I’d like to know whether I should worry that a misstep will bring severe consequences.
Excerpt from Yahoo’s email follows.
Hi Yahoo Member,
We love that you love using your Yahoo Mail. And we want to make sure you always have the best experience. That’s why we’re reaching out today.
We’ve noticed that you’re using non-Yahoo applications (such as third-party email, calendar, or contact applications) that may use a less secure sign-in method. To protect you and your data, Yahoo will no longer support the current sign-in functionality in your application starting on October 20, 2020. This means that you will need to take one of the steps below to continue using Yahoo Mail without interruption.
But don’t worry, you have options. Find an option that works best for you below:
Option 1: We recommend that you access your email using our free Yahoo Mail app for iOS and Android or simply go to mail.yahoo.com to access Yahoo Mail on the web.
Option 2: Keep your current, non-Yahoo app, BUT follow a few steps to get it to sync with our secure sign-in method. The steps vary across different email applications, but in most cases, you will have to remove your Yahoo account from the app and then add it back again to update the sign-in security. Use the links below to follow the specific steps for your current application:
I’ve been through something like this with Yahoo. I think what they want you to do is set up an “app-specific password,” a separate password to be used specifically by whatever third-party mail program you’re using. It’s a bit of a nuisance, but you only need to do it once.
I don’t think your ex is correct about losing all your archived emails. The worst-case scenario is that you’ll have to access Yahoo Mail in a web browser instead of your usual email client.
OK, that’s not what I thought it was going to be, but I’m going to throw this in here just in case even though the wording in the email you got is quite different:
I use Mac Mail with a Frontier email address, and Yahoo took over Frontier quite a while ago. And for several years now I’ve been getting emails claiming that if I didn’t log in at the link and do X I’d become unable to use my email as of date Y.
They all get transferred to junk and deleted, and the only negative result is that after a while I get another batch of such emails, only now the deadline date is later than Y; because Y has long passed and my email’s still working fine.
So the first thing I’d do is to double check – not from any of the links in that email – and make sure that these are actually coming from Yahoo and that you actually need to go through the procedure.
ETA: My email’s archived on my own computer, though (and on separate backups.) So nothing Yahoo takes it into its mind to do can make me lose my archives. You might want to consider that, as apparently you’ve got stuff you don’t want to lose.
I did a little research and found a couple of threads on other boards where people were discussing this (here and here). Apparently it’s for real. However, like you, I recall getting similar emails from Yahoo in the past. Maybe they really, really mean it this time? 
The gist of those two threads I linked is that generating the app-specific password is the simplest option, and doesn’t require removing and re-adding your account. However, “simplest” is subjective and some folks may find that more confusing.
I know that on an iOS device, deleting an account from the native Mail app will delete all the mail from your device. However, doing that doesn’t delete mail from Yahoo’s servers, so I’m skeptical that anything could be permanently lost this way. I understand why people would be anxious about it, though.