How to merge a distribution list into another:
1. Click on the title of the list that you want to merge into another.
2. Click Options > Export all x number of contacts.
3. The file will automatically download, and then you can find it in the Downloads folder.
4. Click Contacts > Import Update > From Outlook CSV
5. Choose file > choose the one you just downloaded :)
6. Overwrite if you feel that there may be duplicates between the 2 lists that you are merging (if you don't want duplicates).
7. Click on the dropdown menu to select the distribution list that you are merging INTO
8. Click Import!
Let us know if you have any questions!