What does USPS require for all letter-size mail to avoid additional charges?

Meeting the aspect ratio is crucial for all letter-size mail to ensure it qualifies for standard pricing and avoids additional charges from USPS. The aspect ratio refers to the relationship between the length and the height of the envelope. For letter-size mail, the aspect ratio must fall within a specific range, which is between 1.3 and 2.5 when calculated by dividing the length by the height. If the dimensions of the mail piece do not meet this criteria, it may be classified differently and subject to higher postage rates.

The other aspects, though important for mailing, do not directly influence avoiding additional charges in the same way. For instance, while clear labeling of weight can be helpful for certain mail classes, it is primarily necessary for packages rather than letter-size mail. Correct addressing format is also essential for successful delivery but does not impact the pricing structure specifically for aspect ratio compliance. Lastly, colors on the envelope do not have a bearing on the additional charges imposed by USPS; they can be a matter of preference or branding. Thus, ensuring that letter-size mail meets the aspect ratio is the key requirement to prevent extra fees.