Occasionally, I have problems sending mail from Outlook 2007 but no problem
receiving email. How do I fix this problem? It hampers me when I work
remotely.

Background:
Outlook 2007 is configured with 2 email accounts from the same ISP on a
laptop running Vista. While at home, I never have a problem sending or
receiving email. I use the laptop on a number of wireless networks but
occasionally have problems sending mail (but no problem receiving). As I
will be working at this location for the next few weeks and I can't send
mail, I need to resolve this issue. This issue also occurs when I am
hard-wired (e.g., hotels, libraries, friends' DSL networks, etc.) but only
impacts outgoing mail ... incoming mail & Internet access works fine. ISP
doesn't know why this is occurring.

Error messages:
Task - Sending' reported error (0x8004210B) : 'The
operation timed out waiting for a response from the sending (SMTP) server. If
you continue to receive this message, contact your server administrator or
Internet service provider (ISP).'

Task - Sending' reported error (0x80042109) : 'Outlook
cannot connect to your outgoing (SMTP) e-mail server. If you continue to
receive this message, contact your server administrator or Internet service
provider (ISP).'

Task - Sending' reported error (0x80004005) : 'The
operation failed.'