Hitachi SINGLE-BAND PCS PHONE SH-P300 - Manual (Page 148)

Section 2: Understanding Your Phone
139 2J: E-mail
The display and editing procedures for unsent e-mail are the same as for
outgoing e-mail, and the same options are available. Refer to the section
dealing with outgoing e-mail for details.
Tip: Once the number of unsent e-mail messages passes 10, the oldest
unsent e-mail is overwritten. However, protected unsent e-mail is not
overwritten.