We found one dictionary that defines the word undeliverable mail:

Art (1 matching dictionary)

1. Glossary of Stamp Collecting Terms (No longer online)

▸ Words similar to undeliverable mail ▸ Usage examples for undeliverable mail ▸ Idioms related to undeliverable mail ▸ Wikipedia articles (New!) ▸ Words that often appear near undeliverable mail ▸ Rhymes of undeliverable mail ▸ Invented words related to undeliverable mail