You're having a phone conference with several people at work. One of the managers says that one of her employees hasn't been getting any e-mails about a certain project. She asks you to make sure that he gets these e-mails. You say:
Sure, I'll add him to the distribution list.
"Sure" means "yes". But it's more casual. Just answering "yes" to a question can sound as if you are angry.
"Sure" also has some of the meaning of "of course" - meaning that it's obvious and expected for the answer to be "yes". But "of course" is a stronger response than "sure".
You use "will" when you're announcing a decision that you just made. In this example, you heard someone say that someone wasn't getting the e-mails. So you decided to add him to the list. If you were already planning to do this, you would say:
Yes, I was going to add him to the distribution list.
Each point on a list is called "an item". When you make a new item for a list, you are "adding" that item to the list.
A "distribution list" is a list of everyone who is supposed to receive something. In e-mail, it's a convenient list of addresses for people who are supposed to get emails about a certain subject. For example, you might have a distribution list for all of the members of a department at work. Or you could create a distribution list for all of the people who are supposed to get a weekly report that you write.
Use "will" to offer to do something, or when you've just decided to do something like in these situations:
("I'll" is short for "I will", of course.)
When you've been planning to do something for a while, don't use "will". Say "I'm ___" or "I'm going to ___".
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