Adding a question mark to ensure a response

It's incorrect to add a question mark because it's not a question. If you wanted to make it a question, you might write, "Would you be interested in more information? Let me know and I can send it" or something along those lines.

If you would say it with a rising intonation at the end, you can represent that with a question mark. However, I don't think making it a statement with a period is too forceful either. You may want to do some research on uptalk and how it is perceived by the people around you, as some people look upon it negatively.

More often than not, when you end a non-question statement with a question mark, it implies incredulity, disapproval, etc.:

"You're going out with him?"

"You ate the whole thing?"

"You did what?"

Better yet, add multiple question marks and/or a few exclamation points:

"You turned down the job??"

"You told him??!?!"

Placing a question mark after that sentence may lead your reader to think that the order of first two words has been accidentally reversed, which will not help your persuasiveness.

It is sometimes acceptable to use a question mark to convert a declarative sentence into a query. However, it is usually considered a casual form: "It's raining?" This is more common in speech than in writing.

If you are pitching an editor your best approach is accuracy in grammar, punctuation and mechanics. If you want to offer more information, do so directly.

I'm afraid the editor to whom you made your pitch was probably negatively impressed. Writing is not speech, especially formal writing. (And even in speech, making a statement with a rising intonation is affective, and quite off-putting to many.)

If you want to ask a question, ask a question. Don't force your reader to guess at your intent, and don't leave your skills and knowledge open to question, as in "Does this person really know how to write?"

Don't worry about the grammar. It's a matter of style and intonation. If you would have asked the question with a rising intonation, why not add the ? If you like that style of speech, you should write that way in an email, which I view as being closer to speech than to a letter or other more fomal writing. Personally, I don'tlike it when Terri Gross makes a statement with a rising intonation, trying to elicit a response from her interviewee. I agree with others who say this is affective and annoying. But that is my preference and should mean nothing to you, who must choose your own spoken, and then written, style. I think the main thing to watch out for is having one style in person and pushing awkwardly to have a different one in your emails. The other thing is that you are in a supplicant position here. You want to send more information. But you need permission. I think your statement is very efficient at getting that point across, and doing so in keeping with the relationship..

I think the internet is changing the way people write, as John comments it's about a style! We throw in punctuation marks, even when they are not needed, to add a voice to our writing... yeah, for some it's irritating, but, if it gets your meaning across isn't it alright to go with the flow???

I can send you more information if you are interested?

This is wrong because it is actually asking the other person to make the decision as to whether you can send more information. Use a period.

I think another option would be: I can send you more information if you are interested, are you ? And I believe what makes it "forceful" is the tense choice. "if you'd like to, would you ?" sounds softer to me. This is an EFL's point of view ...

Steve, I'm not saying that the question mark is correct, but if you use a period, you're still asking the other person to decide.

Is it right, is it wrong, did he care? Likely he read it and answered your question, and then moved on to the rest of his inbox. I really wouldn't worry!