For many months now we have had problems with the SMTP functionality of the POP and IMAP accounts on the Windows Mobile 6.1 devices. Due to changing towers and service, from provider to provider it would mess up the SMTP functionality within Windows Mobile 6.1. There were some small fixes around which would help(or not) temporary. Thanks to the MVP community Microsoft was brought to the attention of this problem and came out with this fix:
http://www.microsoft.com/downloads/details.aspx?familyid=d9d71b2e-d2dd-44f2-86e5-1e53aad7fb7a&displaylang=en&tm
Hopefully this will solve all these problems. Time will tell.
