When sending items to the USA by letter rate, I have had a couple returned to me as unable to deliver over the past 12 months. Both addresses were perfectly valid.

However, a customer has been able to find that USPS use automated equipment to process the post, which only reads the last 4 lines of the address.

Normally, you have :

House Number, Street
City
Zip Code
USA

However, the problem seems to arise where the font size is too large on the labels, so an address such as

301 South Shore LN
Illinois
NE 31313
USA

Appears on the label as:

301 South Shore
LN
Illinois
NE 31313
USA

The machines do not read "301 South Shore " and pass it for manual processing. However with staff cut backs, this doesn't always happpen and the item is returned as invalid address!!

When I print large letter or small packet labels, this does not seem to happen, as the font used for the address is smaller for some reason!