People don't recieve postcards

[gifwav]

I've got problems with the postcardsystem.
When a visitor sends an postcard the recipient don't recieve the mail.
People only recieve a postcard when registered users send the postcard.
And it only works when I use smtp server in the settings of the control panel.
I'm using 4images 1.7.1
Today I've installed 4images 1.7.4 and everything's working fine with this version.
I don't have to use the smtp server.

What could be the problem?
I'm using several mods.

regards,

Jan