While Seniorjudge answered your question (correctly), I answered what you were asking.
Here is your future. Your corporation will get a default judgment against you. They will perfect the judgment and try to collect. You will write a check or try to pay yourself or sell some property and you will find a lien against it or will find the checks don't work any more because of the levy in on the bank account. YOU will now go to the court and claim you were not served. YOU will now try to serve the other party with your motion to set aside the default judgment. This is where the problem comes in. As a matter of law, the other party will provide proof they served you. I know you think they didn't, but they will provide proof. The burden will now fall on you to either prove they lied (It's nearly impossible to prove a negative.) and win on a matter of law, or claim on a matter of equity (fairness) you did not have notice of the suit.
This is where your problem lies. If the other side can provide the letter, it in no way proves, as a matter of law, you were served. But, as a matter of fairness or equity, they can show you did know of the suit.
See how that works? The question you asked was wrong. Understanding the process is what is important. If you think a lawsuit is a cooperative process, why would any defendant who is represented by an attorney who knows EVER "accept" service? Have all the corporate attorneys gone mad? Has Yale law school failed completly? Or, do you have misconceptions about what is going to and must happen?
Info edit:
Also, please see 49.051.