For the new Yahoo Mail (June 2017 version), I cannot figure out a way to copy and paste multiple email addresses when composing a new email. I tried delimiting with semicolons, commas, and spaces, but it only retains the first and last email in the "To" field. For example:
email@example.com; firstname.lastname@example.org; email@example.com firstname.lastname@example.org, email@example.com, firstname.lastname@example.org email@example.com firstname.lastname@example.org email@example.com
Will result in this (only the first and last emails are retained):
This used to work with the previous "Classic Yahoo Mail" (prior to June 2017 version).