Uhm.....you might just be injecting your opinion as to what is, or is not, in this letter.
From the letter (emphasis mine):
For the purpose of establishing friendly relations between the Confederate States and the United States, and reposing special trust, &c., Martin J. Crawford, John Forsyth, and A. B. Roman are appointed special commissioners of the Confederate States to the United States. I have invested them with full and all manner of power and authority for and in the name of the Confederate States to meet and confer with any person or persons duly authorized by the Government of the United States being furnished with like powers and authority, and with them to agree, treat, consult, and negotiate of and concerning all matters and subjects interesting to both nations, and to conclude and sign a treaty or treaties, convention or conventions, touching the premises, transmitting the same to the President of the Confederate States for his final ratification by and with the consent of the Congress of the Confederate States.
It is very clear...the purpose was to agree, treat, consult, and negotiate and everything was on the table. What isn't in this letter is an ulitmatum and veiled threat.
Nonsense. They were there for recognition and recognition only. That vague offer to talk would have happened only after Lincoln capitulated to rebel demands and agreed to recognized the legitimacy of the Southern rebellion. An end to secession wasn't open for discussion. Any of Lincoln's positions were not on the table. Only recognition. And only had Lincoln caved was there a possibility of discussing payment for debt and stolen property...but only if the matter was of interest to the confederacy. By that point, having gotten what they wanted, the odds of serious discussions on those matters was likely zero.
Is that the whole letter? Can somebody give me a link to the reference?