The letter itself, which your excerpt shows to have been written by Marx, opens as follows:
"To Abraham Lincoln, President of the United States of America
Sir:
We congratulate the American people upon your re-election by a large majority."
In other words, the letter, which was written by Marx and signed onto by his commie club, went to Lincoln himself and not the general people as you claim.
It was indeed delivered to the American embassy as that was the means of transmitting it TO Lincoln at the time. The records further show that it was transmitted from the embassy to its intended recipient, Abe Lincoln, in January 1865. Charles Francis Adams, the ambassador at the time, sent a response to Marx and his commie club informing them that the letter to Lincoln "was duly transmitted through this Legation to the President of the United States, has been received by him."
Sir: We congratulate the American people upon your re-election by a large majority. If resistance to the Slave Power was the reserved watchword of your first election, the triumphant war cry of your re-election is Death to Slavery.
At least the IWA knew the fight was about slavery, not tariffs.