Currently, there is no option to disable the email requirement for offline donations (this is because our system identifies donors by their email address, first, and last names). If a donor provides you with an offline donation, and he or she did not provide you with their email address, you will need to enter a modified email address instead. For example, if your donor's name is John Doe, you can input something like JohnDoe@YourOrganization.org.
Just be sure to use a unique email address for each individual donor. Otherwise, using the same email address for each donor will merge them into one donor profile, and it might make it seem as though the same person provided each donation. After this is done, you can also send receipts out to each donor that has been manually entered in Donorbox.