Hey Socko. As will often be pointed out, it depends on the context. If you are talking to someone you know very well, you can use number 1 and it will sound perfectly polite. If you don't know the other person very well or your relationship is simply professional, then number 2 will do. Finally, number three is not something I would "say" but would rather "write" in a formal letter. I would also offer this fine-tuning to your sentence: "If you have any questions about the work (the job?), you can/may contact me." (Your original sentence seems to say that the person who contacts you wants you to offer him/her some questions, not answers!) peace, Mr Spears

Hello, Exactly as Jura says ,more polite and friendly. "Don't hesitate" emphasizes your readiness to help

Number 3, it sounds more polite and friendlier.

Hi Socko Are you trying to be polite to use formal sentences like in a business setting? Or are you trying to be polite to be gracious and courteous by offering your time? I think your 3 examples are equally polite, but they convey other things. #1 is very neutral. People can contact you. #2 is very similar, but you’re giving them permission. So you’re probably a teacher and they are students. #3 is similar to #1, but you’re asking them not to hesitate. If you are equals, then this is an offer to contact you. If you are their boss, then you’re pressuring them slightly to contact you if something is not clear. When writing to someone, to encourage or invite requests for help, I would say: -- You’re welcome to contact me if you have any questions about this work. (“you are welcome to” is an invitation.) -- Please feel free to contact me if you have questions about this work. ("feel free" is said in American English, and is a friendlier version of "don't hesitate" because it is positive instead of negative.) When writing to someone, to offer help but not to encourage it, I would say: -- If you have questions about this work, you can contact me at [email]. -- Please direct questions about this work to [email]. When speaking to someone, to encourage or invite requests for help, I would say: -- If you have more questions, just give me a call. I’m happy to talk to you more. (casual but inviting) -- Feel free to email me if you have questions. When speaking to someone, to offer help but not to encourage it, I would say: -- You can email me if you have further questions. -- For questions about this work, you can reach me by email.

Option number three, "do not hesitate to ask me," has been widely criticized as a hackneyed expression or an annoying cliche. I would avoid using it.