Re: Secondary Email Addresses Not Showing up on Rogers Yahoo Email Online
If you've properly created the other accounts, you should be using the following link, wherein you enter your e-mail address and password. Once at the member centre page, click "mail" at the top right. You'll need to do this separately for each e-mail address you created.
I'm not sure if it's possible to do what you want (signing in once) with your three new e-mail addresses. I believe that only works for forwarded e-mails and/or disposable e-mail addresses that are "part of" one of your e-mail addresses.
Of course, rather than using Webmail, you can use an e-mail client like Outlook (on a computer, etc) and create accounts in that e-mail client that would then "go" to all of those accounts and send/receive your e-mails. You would need to create app passwords for each e-mail account in the client.