Как я настраиваю свои записи MX для надлежащей пересылки почты в мою учетную запись Gmail?

Согласно странице справочника ldap_table (5) возможности:

%%     This is replaced by a literal ’%’ character. (Postfix 2.2 and later).

%s     This is replaced by the input key.  RFC 2254 quoting is used to make sure  that  the  input  key
       does not add unexpected metacharacters.

%u     When  the  input  key  is  an  address of the form user@domain, %u is replaced by the (RFC 2254)
       quoted local part of the address.  Otherwise, %u is replaced by the entire  search  string.   If
       the localpart is empty, the search is suppressed and returns no results.

%d     When  the  input  key  is  an  address of the form user@domain, %d is replaced by the (RFC 2254)
       quoted domain part of the address.  Otherwise, the search is suppressed and returns no  results.

%[SUD] The  upper-case equivalents of the above expansions behave in the query_filter parameter identi‐
       cally to their lower-case counter-parts. With the  result_format  parameter  (previously  called
       result_filter  see the COMPATIBILITY section and below), they expand to the corresponding compo‐
       nents of input key rather than the result value.

       The above %S, %U and %D expansions are available with Postfix 2.2 and later.

%[1-9] The patterns %1, %2, ... %9 are replaced by the corresponding most significant component of  the
       input key’s domain. If the input key is user@mail.example.com, then %1 is com, %2 is example and
       %3 is mail. If the input key is unqualified or does not have enough domain components to satisfy
       all the specified patterns, the search is suppressed and returns no results.

       The above %1, ..., %9 expansions are available with Postfix 2.2 and later.