You don't exactly resync anything, you just add the mail account. If it already exists, it may be in working order. You can send and receive test emails to yourself to determine that. If it's working you're done.
If not working, you'll need the set up details from Sbcglobal to reinstall the Mac account. You should still be able to go to the website to get the data as well as get your mail. If the details you need are not obvious on the website, you'll need to contact Sbcglobal to get them. They may also have tech help to assist you in this.
You might want to consider using iCloud mail. It's a part of your system and it works well. If you just can't get your old email to work , or if all this is just too much or you can't get all the assistance you need for whatever reason, iCloud is a good alternative. https://www.lifewire.com/how-to-create-an-icloud-email-4584873. This is somewhat dated but the process is unchanged
Go here for general instructions: Add email accounts in Mail on Mac - Apple Support
One thing I would recommend is you upgrade your Mac's OS to the latest it can use. If you're running version 11.7, you may be eligible for a later version but that will depend on the year of your Mac. That information can be found by clicking the Apple logo and selecting "About this Mac".
