According to AT&T Customer Support, the unmerging phase of the two providers had no impact on any passwords associated with Yahoo Mail and ATT Mail. If you changed your passwords at the moment, they will remain the same.
As part of the decoupling phase in 2017, your addresses, calendar files, old emails, and information connected with all Yahoo utilities, such as Yahoo Finance and Tumblr, were transferred to your Yahoo Mail account instead of your AT&T account.
To add to the mystery, AT&T recently removed Synacor, the corporation in charge of the www.ATT.net web portal. Verizon Inc. has taken over AT&T's business. Verizon currently operates both the AT&T email and the AT&T webportal systems, thanks to its ownership of Yahoo Inc., which has handled email services and AT&T email users for more than a decade. Currently.com or Currently.att.yahoo.com are the URLs for AT&T's latest co-branded webportal, "Currently from At&T."