Belgium:

The Post Code field accepts a sequence of four numbers.

Ireland:

The Post Code field accepts seven characters in two groups. The two groups of characters must be separated by a space, not a dash.

The letters B, G, I, J, L, O, Q, S, U and Z are not used.

  • The first group of 3 characters always consists of one letter followed by two  numbers (0-9). The third character cannot be W.
  • The latter four characters must be one number (0-9) followed by four letters.

Luxembourg:

The Post Code field accepts a sequence of four numbers.
 

Netherlands:

The Post Code field accepts six characters in two groups. The two groups of characters must be separated by a space, not a dash.
  • The first group of 4 characters always consists of numbers (0-9)  
  • The latter two characters must be two uppercase letters. The combinations SS, SD and SA are not used.

Norway:

The Post Code field accepts a sequence of four numbers.

Finland/France/Spain:

The Post Code field accepts a sequence of five numbers.

Sweden:

The Post Code field accepts a sequence of five numbers in a group of three then two characters. The two groups of characters must be separated by a space, not a dash.
 

United Kingdom:

The Post Code field accepts six or seven characters in two groups. The two groups of characters must be separated by a space, not a dash. The first group can consist of three or four characters. 

The letters C, I, K, M, O and V are not used.