Where do you put the attention line in a business letter?

The attention line on a business letter should be the top line or lines on the inside address:

Mr. John Smith

Customer Service Manager

ABC Company

123 main Street

Anytown, ST 00000

If you don't know the specific name of the addressee, the inside address should be:

Customer Service Manager

ABC Company

123 main Street

Anytown, ST 00000

The attention line on an envelope should use the same format, because:

When an attention line is below the address, automated mail sorting equipment removes the piece from the automated line and it goes into a bin for manual sorting by a person. This can delay the delivery by one to two days, depending on the postal service.