Q: Often, when I write emails to finalize appointments, I end as follows, “Could you please confirm that this appointment will work for you.” Although this would seem to be a question, I am not clear as to whether it really is one and needs a question mark.
A: No question mark is necessary.
Although that sentence is worded as a question, it’s not intended as one. It’s intended as a polite imperative—that is, a courteous command or directive. The speaker (or writer) softens the imperative by framing it as a question.
This is a very common way of expressing a command in a mannerly way.
The Chicago Manual of Style (16th ed.) calls sentences like this “requests as questions,” and says they don’t need question marks: “A request disguised as a question does not require a question mark.”
The Cambridge Grammar of the English Language calls this form of expression an “indirect speech act,” one in which meaning is conveyed indirectly.
The authors, Rodney Huddleston and Geoffrey K. Pullum, use as an example the sentence “Would you like to close the window.” As they explain:
“Syntactically, this is a closed interrogative, and in its literal interpretation it has the force of an inquiry (with Yes and No as answers).” But in practice, they say, it’s “most likely” a directive, a request to close the window.
“Indirect speech acts,” the authors write, “are particularly common in the case of directives: in many circumstances it is considered more polite to issue indirect directives than direct ones (such as imperative Close the window).”
Clearly, a sentence like yours—”Could you please confirm that this appointment will work for you”—is neither a question nor a demand. It lies somewhere in between, which is why a question mark (and certainly an exclamation point) might seem inappropriate.
Still, we would not call a question mark incorrect here—just unnecessary. The use of a question mark instead of a period would make the request sound even more tentative, an effect you might not want.
If you wanted to make the request firmer but still polite, you could use a straight imperative, refined with a “please,” as in “Please confirm that this appointment will work for you.”
from Grammarphobia http://www.grammarphobia.com/blog/2016/08/to-be-or-not-to-be-a-question.html