Here are the outlook/outlook express error codes we know about:
Error Message
Possible Cause
Remedial Action
691
Access denied because user name and / or password was rejected or Access denied because username and/or password is invalid on the domain This error can occur if you use a bad username or password; remember in most instances the password is case-sensitive - you will not see the password, so check if Caps Lock is on etc
0x80004005
An unknown error has occurred account [accountName] server pop.[yourISP], Protocol: POP3 port 110 secure(SSL): No Socket Error: , Error Number 0x80004005

If you get this error code, please let us know.

Note: The following suggestion to remedy this has been put forward (please note that this has not been verified): "temporary solution; by changing the port to 109 then hit send and receive you will get another error. Close that box, go back and change port back to 110 and it works fine as long as you don't shut down. Still looking for a permanent fix, everyone says its the firewall but i'm not so sure."

0x800420CD
Cannot send message as one of recipients addresses rejected by the server Check the email address being sent to (no additional dots or spaces). Send your self-an e-mail; if you receive it the recipients e-mail may have a problem.
0x800420CD / 0x800CCC90
Message number 16 could not be retrieved. Account: pop.[yourISP]' Server: 'pop.[yourISP]' Protocol: POP3 Server Response: 'Body nazis: Hard-core exercise and weightlifting', Port: 110 Secure(SSL): No Server Error: 0x800CCC90 Error Number: 0x800420CD

Message cannot be downloaded from server due to known bug in Outlook Express (any Non Microsoft email package will retrieve message) so delete email off the server.

0x800C012E
Outlook Express could not be started. It may not be installed correctly. Make sure that disk is not full or that you are not out of memory. Contact Microsoft support for further assistance. (0x800C012E) Outlook Express *.dbx mail files may be set to read only. Click Start, point to Find, then click on Files or Folders, In the Named box, type "*.dbx", in the Look In, C drive, then Find Now / Right click each *.dbx file, click Properties & clear the Read Only check box. Click Apply, then Close. Note the *.dbx files should only have Archive checked.
0x800C013B
An unknown error has occurred Server: 'smtp.[yourISP]' Protocol: POP3 Port: 0 Secure(SSL): No Error Number: 0x800C013B This may be an error in YPOPs or Yahoo. Check the YPOPs log file and any html files in the same folder.

If YPOPs and Yahoo appears to have worked correctly, this behavior can occur if the Sent Items.dbx file is damaged. Try the following: click Start / Find / Files or Folders type in "outbox.dbx", press Find Now / Edit / Select All / File / Delete and restart your computer (Delete outbox). If this fails reinstall Outlook Express
0x800CCC13
A TCP/IP error occurred while trying to send data to the server. Subject: XXXX Account: 'XXX.XXX.XXX', Server: 'XXX.XXX.XXX', Protocol: XXX, Port: XXX, Secure(SSL): No, Socket Error: 10060, Error Number: 0x800CCC13 Shut down any firewall and anti virus software. Try send/receive. If that doesn't fix it, check your YPOPs log file. If it looks normal, try deleting your effected messages from your outbox and recreate.
0x800CCC0D
The host XXX.XXX.XXX could not be found. Please verify that you have entered the server name correctly. Account 'XXX', Server, 'XXX.XXX.XXX', Protocol: XXX,Port XXX, Secure(SSL): No Socket Error: 11001, Error Number: 0x800CCC0D Please verify that you have entered the server name correctly. If you are using localhost, change it to 127.0.0.1.
0x800CCC0E
The connection to the server has failed. Account: 'accountName', Server: 'XXX.XXX.XXX', Protocol: XXX, Port: XXX, Secure(SSL): No, Socket Error: 10061, Error Number: 0x800CCC0E

YPOPs! has aborted the connection for some reason. Usually due to a Yahoo error, but it might also be a bug in YPOPs. Consult YPOPs' log file and any html files generated to see what happened.

0x800CCC0F
Your server has unexpectedly terminated the connection. Possible causes for this include server problems, network problems, or a long period of inactivity. Account: 'accountName', Server: 'XXX.XXX.XXX', Protocol: POP3, Port: 110, Secure(SSL): No, Error Number: 0x800CCC0F
0x800CCC78
The message could not be sent because the server rejected the sender's email address. The sender's email address was 'something@something.something'. Subject 'hnei', Account: 'Geocities', Server: 'mail.geocities.com', Protocol: SMTP, Server Response: '550 rejected: cannot route to sender <something@something.something>', Port: 25, Secure (SSL): No, Server Error: 550, Error Number: 0x800CCC78 The server does not recognize the senders email address as being valid. Invalid email address in the mail profile. Tools / Accounts / Properties / General. Check email address is correct - whatever@[your Yahoo domain]
(e.g. whatever@yahoo.com).
0x800CCC79
The message could not be sent because one of the recipients was rejected by the server. The rejected email address was 'XXX@XXX.XXX'. Subject 'some subject', Account: 'pop.[yourISP]', Server: smtp.[yourISP]', Protocol: SMTP, Server response: 550 Cannot route to <XXX@XXX.XXX>', Port 25, Secure(SSL): No, Server Error: 550, Error Number 0x800CCC79
0x800CCC7D
The Server does not support a SSL connection, Account pop.[yourISP], Server: smtp.[yourISP], Protocol SMTP, Server Response: '250 HELP', Port 25, Secure (SSL): Yes, Server Error: 250, Error Number: 0x800CCC7D Click Tools / Accounts / Mail / Properties / Advanced - remove tick from secure SSL connection.
0x800CCC90 / 0x800CCC92
Problem logging onto mail server - Your password was rejected - Err authorization failed Click Tools / Accounts / Mail / Properties / Servers - check account name and password.
0x800CCC90 / 0x800CCC92
Err unable to fork This error should not occur with YPOPs!. Contact us if you get this error.

If you encounter an error that is not in the above list, or know of one we are missing, please let us know (create a new topic in the YPOPs!/Windows forum).