E-mail Problem

[#1]

I use Mozilla Thunderbird for e-mailing, with Mailwasher Pro for seeing what e-mails are coming my way. Everything works fine, except for when I receive e-mails from one friend. I can see and read his e-mails in Mailwasher Pro, but when I download them into Thunderbird, they show up in the temporary window which tells me which e-mails Thunderbird is downloading, but never actually end up in the In Tray. From that point they seem to have disappeared. Certainly, I am unable to find them.
Any suggestions, please?
TIA

[#2]

An update - I have found the missing e-mails. They are in the In Tray but instead of having a date stamp of 19/01/2012, they have a date stamp of 18/11/2011.
How has that happened?

[#3]

your friend probably need a new clock battery in their PC

[#4]

Thankyou Pierre_Pierre. I will advise my friend accordingly