About custom fields and data types

You can use custom fields in several ways in Outlook.

You can create new data-entry fields for a view or form so users can add their own custom information. For example, you can create a Date/Time field named "Last Talked To" in a contact folder and then add the field to a Phone List view.
You can create new views by combining the standard fields in a single column. For example, you can create a column that combines the State and Country fields in an address list to save space.
You can create a formula field to show information in a new way. For example, you can create a field that displays "Large" when a message is more than 10,000 bytes and "Small" when a message is under the same limit.

Any field that you create is stored in the folder in which you create it. To use a field in more than one folder, you must recreate the field in each folder.

You can create and view custom fields in table views and card views. You can create custom fields with the following data types in Outlook.

Data type	Use to represent
Combination	Combinations of values of fields and text in a column (table) or row (card). You can specify whether to show each field or show only the first non-empty field. You can also combine text with fields without the use of quotation marks.
Currency	Numeric data as currency or mathematical calculations that involve money.
Date/Time	Date and time data.
Duration	Numeric data. You can enter a duration as minutes, hours, or days. Values are saved as minutes.
Formula	Calculations based on standard and custom fields. You can use any appropriate functions and operators to complete the formula.
Integer	Non-decimal numeric data.
Keywords	When filled in, this user-defined field is used to group and find related items similar to the way the Categories field is used in Outlook. Text with multiple values to be separated by commas. Each value can be grouped individually in a view.
Number	Numeric data or mathematical calculations except those that involve money. (For money, use Currency data type.)
Percent	Numeric data as a percentage.
Text	Text or combinations of text and numbers, such as addresses. Can be up to 255 characters long.
Yes/No	Data that contains only one of two values, such as Yes/No, True/False, On/Off.

Each of the data types except Combination, Formula, and Keywords has a series of standard formats you can use to show the values of the fields.