You can use Outlook 2013/2010 to bring contacts from other email accounts (or address books) into your Office 365 account.
Important: If you use Outlook Web App and Outlook 2013, 2011, or 2010, to connect to your Office 365 account, you will only need to import these contacts once using any of these clients. Once imported, they will be available to you in the other clients.
How do I import contacts using Outlook 2010?
The most common is Comma Separated Values (Windows), also known as a CSV file. If you are importing contacts that were exported from Outlook to an Outlook Data File (.pst), click Outlook Data File (.pst).
This usually is the Contacts folder unless you have multiple accounts, or have created multiple contact folders for an account.
You will now see a screen similar to the image below. The "Values" column on the left side displays the items that you are importing. The right side has two columns. The "Field" column represents fields in your Outlook address book, and the "Mapped from" column shows which data will fill each field. For example, if the field E-mail 1 is mapped from the value Business E-mail, your contact's business email address will show up in the first email address field once it's imported to Outlook.
To make sure your contacts import correctly, make sure that the items in the "Mapped from" column are consistent with items in the "Field" Column. You will have to click on the plus sign () icons to expand items in the "Field" column. To designate a field for a given value, simply drag the item from the "Value" column to the "Field" column.
In the example below, The name fields do not have anything in the "Mapped from" column. If these contacts were imported as is, none of the contacts would have names in the Outlook address book.
After dragging the values Title, First Name, Middle Name, and Last Name to the right hand side, the names will import correctly. This process should be repeated for email addresses, and any other piece of contact information that you want imported.
For assistance with exporting from your email client, please click here.