Professionally Indicate a Misspelling

I am writing a formal letter to a business colleague, and I know that I may have misspelled someone's first name. I do not have a way of checking if my assumed spelling is correct, but would like to at least acknowledge that I may have misspelled it.

I will often see such errors acknowledged like this:

misspeeled (sp)

misspeeled (sp?)

Is there a better way I can professionally acknowledge this possible error, since all other means of verifying its spelling have been exhausted?

Solution 1:

For me, the (sp?) method has connotations of school homework. Although it's a little long-winded, if it's only to be used once in the letter I would prefer (my apologies for any misspelling).