First let make sure you have the most resent version of the update.
From the main screen, touch menu tab
Touch About Phone
Touch System Updates
Then could I get you to do a soft reset on the device.
Press the Power key.
Touch Power off.
Press the Power key to power on the device.
Then dial *228 send and option 1 on the device.
Also try making sure the messages being sent to the device from emails are less than 160 characters.
Some EMS (Extended Length Messages) are not supported by the device. SMS messages in excess of 160 characters are converted to MMS messages. There sometimes is a compatibility issue with the phone and email account. Try sending an email message from another email account. Also try sending a message directly to your Gmail account.