Text data types and Memo data types are variable length fields. Their length depends on that particular piece of data entered into it. The limits for Text are 255. But if you type in 5 characters, then it is stored as 5. Memo can handle 64,000. Again, it only stores what is typed in. This is for Access 2000 by the way.
I don't know any email addresses that are 255 characters. So a text box is fine. Daily activites you could write a book so a memo field might do.
Neil