There is not an exact number of contacts that you can add in a distribution list (DL), the limit is based on the total size of the contacts. If you use the very basic information for contacts (for example, only the name and the e-mail address), your DL limit may be 125 to 130 contacts. On average, the number of contacts that you can add to a DL is limited between 50 and 70 contacts, but for some user who have contacts that contain a large amount of data, the DL limit can only be as little as 25 contacts. The DL limit is also based on the property size limit of the Microsoft Exchange server. The property size limit for an Exchange server is about 8 kilobytes (KB). The Exchange server stores all contact links in one property store, so the DL limit depends on the contact's name length and the size of the entry ID (the type of e-mail address and the length), on average. Keep this in mind when creating a large list. You may want to use List A, List B. etc.

A way to overcome this DL limitation is to create another distribution list containing the List A, List B, etc. distribution lists so it is only necessary to send one email to the recipients.