Microsoft has released a patch for Windows Mobile 6.1 that fixes problems with sending email in case of an unspecified SMTP server. Here’s what they say:
This behavior is associated with a feature that is introduced in Windows Mobile 6.1. The feature allows for mobile operators to specify an alternate SMTP server name that is used if e-mail messages cannot be sent by using the user-specified SMTP server name. If the mobile operator does not specify an alternate SMTP server name and if the Windows Mobile 6.1-based device does not connect, the e-mail account is corrupted and cannot send e-mail messages.
The patch can be downloaded from Microsoft’s website and installed either from the ActiveSync connected PC or directly on the device. Here’s the link to the page with more information.