An email address ending in “@ymail.com” was a valid email address when Ymail was an active email service provided by Yahoo!. This service allowed users to choose a “@ymail.com” domain name instead of the standard “@yahoo.com” domain for their email addresses. For example, if a user chose the username “example,” their Ymail address would have been “example@ymail.com.”
The introduction of alternate domain names like “@ymail.com” aimed to provide users with more options and potentially alleviate the scarcity of desirable usernames on the primary “@yahoo.com” domain. This strategy offered a simple way to expand the address space available to Yahoo! Mail users, and provided a shorter alternative to the traditional yahoo.com address. While offered, the main benefit was simply more availability for user names.