According to the Delaware Secretary of State, you may return your absentee ballot to the Department of Elections office in your county:
Kent County Department of Elections: 100 Enterprise Pl Ste 5, Dover DE 19904 (source)
Phone: (302) 739-4498
Email (Absentee Voting): absenteekc@delaware.gov
Email (Vote By Mail): votebymailkc@delaware.gov