Lookup for "220 4.1.4"
Temporary Error - This status code indicates a transient issue and may resolve itself.
Basic Status Code Details (220)
Enhanced Status Code Details (4.1.4)
Destination mailbox address ambiguous
The mailbox address as specified matches one or more recipients on the destination system. This may result if a heuristic address mapping algorithm is used to map the specified address to a local mailbox name.