I supose it should say mail and not "main"

Signed-off-by: Suki <suki@missallsunday.com>
#1381 create a unique txt string for personal messages
and replace the "message" for "post" in $txt['error_no_messages_in_time_frame']

I couldn't find the reference to that txt string in personal messages to create a unique one for it as well

Signed-off-by: Suki <suki@missallsunday.com>