My wife has an HP Desktop using Windows 7 and email client of ATT and Yahoo

sending , receiving or both?
not told who;s email service is it of 1000's (i run my own)
tops are(not me) gmail.com , live.com , yahoo?,and more...
using #1
web mail
or #2

GREAT EMAIL CLIENT APP. LIKE THUNDERBIRD OR OUTLOOK
THE ANSWER IS.
FOR Client apps, do it there in the app,click fonts.(click help)
for web mail online ask them at their web site.
Email is tricky if you have HTML turned on .
the content is controlled by the sender not you. (but depends on if web mail or client app usage)

also is this windows./? not told
but windoz has , settings for the visually Impaired. (in lots of ways)

https://helpdeskgeek.com/windows-10/windows-10-accessibility-features-for-disabled-people/


if not visually impaired, go to your web mail site
and ask them.
not told yours, so answers can only be vague to useless.
there is no FONT GOD yet;.

In what sense, are you using an email client extension, just going to att.net? Have you tried to login via yahoo.com instead?

Which email account ?

Erase Email Addresses in My Computer

Email addresses can be stored on a computer if you use email software, such as Microsoft Office Outlook and Yahoo Messenger Beta.

Deleting email addresses manually from these programs does not actually completely erase them from your computer.

To erase email addresses permanently, meaning that a hard drive recovery program will not be able to restore them if it is used, requires a process called formatting, which completely erases the information on a hard drive.

Click on the shortcut "My Computer," which you can locate on your desktop.

Right click "Local Disk (C:)" and select the "Format" option.

Change the "Allocation Size Unit" to "Default Allocation Size."

Click the "Start" button.

The email addresses, as well as the rest of the files on the hard drive, will now be erased.

Delete a Live Mail Email Address

Windows Live Mail is a part of the Windows Live suite of productivity and entertainment programs, and it is intended to be the new free email client for Windows beginning with Windows 7.

After trying Windows Live Mail, you may decide that you have added too many email addresses and that you would prefer to use the email client to check only one address.

Remove an email address from Windows Live Mail to reduce the clutter in your email inbox.
Launch Windows Live Mail, and browse to the "Tools" menu at the top of the screen.

Click "Accounts."

Click the email account that you would like to delete.

Click the "Remove" button.

A message will appear to remind you that any messages belonging to the email account that are not backed up in another location will be deleted permanently.

Click "OK" to confirm.

The account will be deleted immediately.

Click "Close" to return to Windows Live Mail.

Delete Hotmail Adresses

Log in to your hotmail account and click "Help."

Search for "Cancel Account" and select "Why are all my email messages gone?"

Expand the option that says "Close a free Hotmail account" and click "Windows Live Hotmail close account."

Click "Close Account" on the page that opens.

If you do not sign in to your account for 365 days, your account will also be deleted.

Hope this helps.

Hi,
When a person is using the ISP (Internet Service Provider) for the e-mail, and that provider is changed, the e-mail goes with the provider. One cannot have a sbc e-mail account without sbc being the carrier.
One could contact sbc to find out if they could forward those unread messages to the ATT e-mail account.
Hot mail from Microsoft or G mail from google are supported by the Internet Browser, so those accounts will transfer from any different ISP.
Wayne.

You cannot configure Yahoo account with Windows live mail.
And the reason you are getting the error because you have Micosoft outlook in the pc and that email client (MS outlook) is not configured with your yahoo mail and it is not the default email client in your PC. Windows live mail is the default email client in your PC and you cannot configure Yahoo account in windows live mail.

If you looking for POP3 SMTP Mail Servers then it would be
AT&T WorldNet incoming mail server: postoffice.worldnet.att.net
AT&T WorldNet outgoing mail server: mailhost.worldnet.att.net
or
incoming mail (POP3) -> ipostoffice.worldnet.att.net

Just for POP, I think should be somethinnd like
[email protected]
or
pop.att.yahoo.com

Incoming Mail Server (POP3):
Host Name: ipostoffice.worldnet.att.net:995
User Name: [email protected]

Good luck

If you use Yahoo! Mail for all your email needs, some of the amenities of Windows seem to elude you. A click on an email link in your browser brings up Outlook Express or another desktop email program, not a new message in Yahoo! Mail. Trying to send a file directly from Word, OpenOffice.org or another office application yields the same, unsatisfactory result.

Fortunately, the state of dissatisfaction need not be permanent. It will be overcome by making Yahoo! Mail act as your default email program in Windows, which, if you use Windows 95 or later is an easy thing to do.
Make Yahoo! Mail Your Default Windows Email Program

To set up Yahoo! Mail as your default email client in Windows:

* Download and install Yahoo! Messenger.
* Select Tools | Internet Options... from the menu in Internet Explorer.
* Go to the Programs tab.
* Make sure Yahoo! Mail is selected under E-mail.
* Click OK.

Yahoo! as Default Email: Does Not Work under Windows Vista

Unfortunately, Yahoo! Mail as your default email program may be hard-wired to use Internet Explorer instead of your default browser, and it does not work in Windows Vista.
Make Yahoo! Mail the Default Email Composer in Mozilla Firefox

In Mozilla Firefox, you can turn to the Mailto 2 Webmail script for Greasemonkey to have Yahoo! Mail handle email links (even under Windows Vista).

http://email.about.com/od/yahoomailtips/qt/et_default_mail.htm

1. Open your email client program.
2. Locate the email account settings for your particular client.
3. Change the POP server to pop.att.yahoo.com.
4. Change the SMTP server to smtp.att.yahoo.com.
5. Check the option labeled Use an encrypted connection (SSL) and change the SMTP port to 465.
6. Check the option labeled Use an encrypted connection (SSL) and change the POP3 port to 995.
7. Confirm the above settings then click OK.