The message(s) could not be sent - Windows Mobile 6.1 SMTP email bug

I came up against this message yesterday when trying to send an email through gmail from my Samsung Omnia:

The message(s) could not be sent. Check that you have network coverage and that your account information is correct. Then try sending again.

Sending email had worked before but now didn't. I checked all the smtp settings and they were all correct. A bit of web-hunting found that this is a problem with all Windows Mobile 6.1 devices - if at any time a connection to the smtp server fails for some reason, the email account gets corrupted and will no longer send email. The account would then have to be deleted from the device and set up again from scratch.

There are unofficial fixes for this around on the web to avoid having to re-setup the email account but Microsoft have released an official patch which just involves downloading a .cab file from here and installing it on your mobile.