The theme for Sunday Stamps today is the post, letters, post boxes, etc.
I'm happy to find 4 related stamps in my collection:
From Netherlands, I have this postcrossing.com stamp issued in 14 October 2011 by PostNL.
The 'Posta Italiana', issued in 7 July 2009. According to the Poste Italiane website, the design "features an envelope taking off, leaving behind a trail formed by the colors of the Italian flag."
This stamp was issued by the Česká pošta in 9 October 2011 to commemorate
the annual World Post Day.
A commemorative issue on 3 August 2012 by the Office National des Postes Tunisie
for the Arab Post Day.