Invalid argument supplied for foreach() in C:\Program Files\Apache Group\Apache2\htdocs\base\modules\user.module on line 174.

Hi.

I am getting couple of errors.
I am new to drupal and php. I have no idea what these errors are.
Please help.

Type php
Date Tuesday, September 13, 2005 - 23:56
User Anonymous
Location /base/?q=user/password
Message mail() [function.mail]: SMTP server response: 503 5.0.0 Need RCPT (recipient) in C:\Program Files\Apache Group\Apache2\htdocs\base\modules\user.module on line 374.
Severity error

Type php
Date Tuesday, September 13, 2005 - 23:56
User Anonymous
Location /base/?q=user/password
Message array_flip() [function.array-flip]: The argument should be an array in C:\Program Files\Apache Group\Apache2\htdocs\base\modules\massmailer\plugins\massmailer_rolelists\massmailer_rolelists.module on line 62.
Severity error

Type php
Date Tuesday, September 13, 2005 - 23:56
User Anonymous
Location /base/?q=user/password
Message Invalid argument supplied for foreach() in C:\Program Files\Apache Group\Apache2\htdocs\base\modules\user.module on line 174.
Severity error

Type massmailer role
Date Wednesday, September 14, 2005 - 00:02
User Anonymous
Location /base/?q=user/register
Message An error occured. The list authenticated user may not have been created.
Severity error

Type user
Date Tuesday, September 13, 2005 - 23:21
User Anonymous
Location /base/?q=user/password
Message Error mailing password to at .
Severity error

I have
Drupal 4.6.3

Please let me know.
Thanks.