When parsing email messages with PHP's IMAP extension there is a response object for each address with the following format.
Returns an array of objects. The objects properties are:
* mailbox - the mailbox name (username)
* host - the host name
* personal - the personal name
* adl - at domain source route
However, I can't seem to find any examples of what the ADL actually is or when it is used.
It's an obsolete "at-domain-list". It must be accepted but no longer used. - @mkaatman