E-mail error cation

Gmail will no longer accept 'pop' remote access to accounts. You have to logon to the account via your browser and read your mail.

could be an incorrect e-mail address
call the receiver and ask them to send an e-mail to you then reply to that e-mail by clicking on the reply tab
tell them to use subject test one so that you know who it is from

I have never seen an email address with two .coms...
One is usually sufficient.

email address you are sending might be not correct or inactive

One problem is that the incoming (POP) mail server shown in the error message appears to be incorrect. The server address should be "pop.att.yahoo.com" (with a period between "att" and "yahoo"). The incorrect mail server address may interfere with authentication of the sender's email address, which is needed before the outgoing message is sent.

The "530 authentication" message indicates your outgoing (SMTP) server likely requires "server authentication". Also, the "Port 25" message indicates your email program is currently trying to send via Port 25, with no SSL; but Ameritech/Yahoo accounts appears to use Port 465 with SSL enabled.

See more on sever settings for "ameritech.net" users:
http://www.dslreports.com/faq/5535
https://motorola-global-portal.custhelp.com/app/answers/detail/a_id/61941/~/i886---at%26t,-bellsouth,-sbcglobal,-ameritech-email-settings

I would suggest you check the settings for your Ameritech email account in your email program. You may need to correct several settings. The steps to access account settings are somewhat different for various email programs (Outlook, Windows Live Mail, Thunderbird, etc.). You should be able to find guidance in the "help" section of your email program.

Try checking the SSL checkbox for outgoing server.

Looks like their spam filter is stopping your mail.

the message could not be sent because it rejected as the the sender

0x800CCC78 SMTP_REJECTED_SENDER Unknown sender. This is caused by having the incorrect e-mail address in the Reply-To field.

You may have to authenticate in outlook express by putting in the SMTP server name of your internet provider instead of yahoo
for example
Incoming = smtp.mail.yahoo.com
Outgoing = smtp.yourISPservername
Some isp's will not let you send out with a different smtp server than theirs.
It's why you can receive but not send.

the message could not be sent because it rejected as the sender