After update to 16.73 Outlook for Mac, Yahoo mail keeps re-syncing and reloading. Changes made in Outlook AND Yahoo are not syncing.

I have had no problems with Thunderbird at all. It takes time to customise it to how you like it. One must remember that it is open source and relies on donations to fund it so one does not have the support and updates that MS Outlook has! Haha! I have no experiece with it's local folders as I run IMAP which leaves everything "safely?" on the Yahoo server which I have used for decades without issue. I am a private user and don't use it for business so volume is fairly light and I am not sending thousands of marketing or spam emails. This also enables you to try different email clients easily and get rid of the ones that don't work for you. I tried Mainspring but did not like it. It seems to require that you join their cloud for some functionality but I did not use it long enough to have to much more to say about it. I don't know Postbox. Happy hunting for a client and let us know if you find something good. I am still in the market for a good client.

I have read a number of negative experiences with Thunderbird recently and am thinking twice about it. Lost and unrecoverable emails being the biggest issue. The comments also claim that Thunderbird has not been updated frequently and the recent updates have made the interface worse, among other things. I am now looking at Mailspring and Postbox (but may circle back to Thunderbird anyway). Anyone have any thoughts on any of these?

About migrating to Thunderbird: If you are using IMAP and all your emails are on the Yahoo server its easy. As soon as you have installed Thunderbird and you set up and sign into you email accounts all the emails are visible and accessable to you. After that it would be a matter of turning local folders on and waiting for all the emails on Yahoo to sync and place a copy on your computer. I don't use local folders at all so I have no hands on experience with local folders so I can't report on more details. Thunderbolt has a lot more user customization and tweaks and add-on's that Outlook does not have so it makes it possible to set it up to your workflow preferences. I use a lot of folders and put away emails I am finished with all the time. Outlook allowed me to do that but a Thunderbird add-on called Quick Folder Move outshines what Outlook can do even allowing you to jump to folders and automatically mark the email as read when it moves it to the folder. This ability is whats missing in Apple Mail (which I would probably use by choice and did use for a long time) and in many mail clients for Mac.
Hope this helps.

Apple will be beefing up their email with the upcoming iOS and OS releases, and I am hoping it is enough for me to migrate completely over. I guess Thunderbird is the alternative, but I have also searched some other alternatives which are promising, but they are paid - not a deterrent for me. Thunderbird and AppleMail are free. I DO have local folders for Outlook, which is one of the main issues of not leaving Legacy Outlook.... does anyone know how well/easy it is to move over to Thunderbird from Outlook Legacy?

Outlook for me has never been perfect. For instance, my own employees whose emails reside on the same server - one of them ALWAYS goes to spam. I have whitelisted at the server level as well as within Outlook to no avail. Similarly, I have a few clients' emails that no matter what I do, go to spam, but I have dealt with these issues through toleration. This constant syncing and unsyncing problem is unbearable and since it will clearly not be fixed I am going to jump ship once I find an alternative I am satisfied with.

BTW - Microsoft is reportedly coming up with another tier of paid service that will include AI in Office - to whatever degree it may have already started to include it. I am sure they are spending their time on that and not on us piddling Mac users with their legacy email.