Subaddresses in aliases

As background on the purpose of subaddresses, the MTA interprets a  character  in an address specially: in an address of the form    the MTA considers the portion of the mailbox after the plus character a  subaddress. If the MTA tells the Message Store to "trust" that subaddress as a folder name for delivery purposes (see in particular the   channel option, and the   channel option),  then Message Store too will treat the subaddress specially, delivering straight to that folder.1

When looking up an alias, the use of subaddresses introduces an extra factor. The MTA&#x27;s "l" channel, or any channel marked with  the   channel option, will try looking up aliases.

Subaddresses in aliases are handled as follows. By default, (that is, with the   channel option explicitly or  implicitly on the channel doing the alias lookup), the MTA first checks  for an alias entry including the subaddress; if no such entry is found,  the MTA next checks for an entry with an asterisk, , in  place of the subaddress. Finally, if there is no prior match, the MTA checks for an entry without any subaddress. For instance, alias entries adam+privileged:  system adam:             bob+&#x2a; carl+special:     system carl+&#x2a;:           david+&#x2a; carl:             eric cause the MTA to translate adam+privileged to system, and adam to bob (note the special case handling whereby the MTA removes the trailing  subaddress character, , from the translation value    if there is in fact no subaddress), while  adam+talklist, adam+general, etc., will be translated to  bob+talklist, bob+general, etc. carl+special will be  translated to system and carl to eric, while carl+talklist,  carl+general, etc., will be translated to david+talklist,  david+general, etc.

This handling of subaddresses during alias lookups is configurable; see the   channel options for configuration at the channel level,   or for aliases stored in LDAP see the (new in MS 8.0) domain-level control available via the   MTA option.

1Note that the   channel&#x27;s  support for folder delivery can be disabled via the  FILEINTO  -channel-specific option.

See also:
 * subaddress_char MTA Option
 * fileinto Option
 * deliveryflags Option
 * FILEINTO ims-ms-channel-specific option
 * aliaslocal Option
 * subaddressexact Option
 * ldap_domain_attr_subaddress MTA Option
 * Aliases