Sometimes a design is not up to the designer or the client. When sending mail through the US Post Office there are certain rules and regulations about size, shape, and weight that must be followed in order to get your mailing piece delivered. And how about things like where you put the return address and a logo on an envelope? Are there hard and fast rules or simply preferred methods. That's the topic of discussion in the forum.
"I want to put the logo at the top corner and the return address at the bottom corner, but it will fall within the OCR area. Is this going to cause problems? Do I have to limit the design to the tiny little upper corner? Boring!"
Seems there's some disagreement among some designers and some USPS reps. From what I can find, the USPS has rules on the recipient's address but for return addresses, it's more like tips and suggestions rather than "you must do it this way" but the return address in the upper left front corner is the norm. A lot of the rules about size, shape, and placement of addresses is more about whether or not the piece can go through postal machines or not. Mail that doesn't fit certain standards has to be processed by hand (which can increase costs for bulk mailings and possibly delay delivery a bit).
From the USPS Quick Service Guide:
Return Address (602.1.5)
A return address tells the USPS where the sender wants the mail returned if it is undeliverable.
A return address is required on certain types of mail. Preferred return address placement is the upper left portion of the mailpiece or the upper left part of the address area--on the side of the piece bearing postage. Mail qualifying for Nonprofit Standard Mail prices must have the name and return address of the authorized nonprofit organization either on the outside of the mailpiece or in a prominent location on the material being mailed (inside the mailpiece)
In the case of designing envelopes for use by a business customer, it seems that a lot would depend on how they plan on mailing those envelopes. Some creative designs might be fine for the occasional letter but if the company uses metered mail, bulk mailing, and other special services then their envelopes need to meet stricter criteria -- including things like return addresses and logo placement.
At the bottom of this USPS page you'll find an image of an envelope with parts in dark and light shading. The dark shading indicates areas of the envelope considered "free space" while the lighter shading is "preferred clear zone to enhance readability." There may be more leeway for logos and other design elements than you might think. Chime in with your own experience both in the US and other countries.
Related: Envelope Design