Outlook gives me this error (I mainly test with Thunderbird though)...
Suggestions on how to determine if the web server/IMAP service is down?An unknown error has occurred. Account: 'account@domain.com', Server: 'mail.example.com', Protocol: SMTP, Server Response: '421 Cannot connect to SMTP server xx.xxx.xxx.xx (xx.xxx.xxx.xx:xx), connect error 10060', Port: 25, Secure(SSL): No, Server Error: 421, Error Number: 0x800CCC67