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alias – Alias Expansion

Last updated March 2020

The alias module lets you rewrite the recipient addresses of messages passing through Momentum. It is similar in spirit to sendmail's /etc/aliases, but alias expansions can be stored in any backend supported by Momentum's datasource layer. “ds_core - Datasource Query Core”

When the alias module is loaded, alias expansion is disabled by default. The Alias_Schemes option, a list that can be specified in the Domain or Global scopes, enables the list of schemes that will be used to expand recipient addresses in that domain in decreasing order of preference. Expansion of a recipient address stops after the first alias scheme that yields a non-empty expansion for that address; the original address is replaced in the recipient list by the address(es) in the expansion. To prevent loops, a recipient address that has been expanded cannot be added back to the list of recipients as the result of expanding another recipient address.


A Scheme is specified in an alias module. The mandatory cache parameter specifies the datasource cache that will be used as the backend, in this example aliasdb. The mandatory query parameter specifies the query string that will be used. The map dictionary specifies the alias map used to construct the bind variables used together with the query string; though technically optional, it is almost certainly necessary. The optional column parameter specifies the name of the column containing the results of the expansion; it may be omitted if the query only returns a single column. All the values (if any) in the results column must be valid email addresses.

alias "alias1" {
  Scheme "myscheme" {
    query = "SELECT expansion FROM foo WHERE address = :address"
    cache = "aliasdb"
    map = [
        address = "%{rcptto}"
Datasource "aliasdb" {
  uri = ( "sqlite:/path/to/sqlite.db" )
Domain "" {
  Alias_Schemes = ( "myscheme" )

A map dictionary is specified by the map option. It may contain any number of arbitrarily named variables; macro expansion is performed on these, with the substrings %{localpart}, %{domain} and %{rcptto} being replaced by the local part, domain and complete address of the recipient being expanded, respectively. No other substrings of the form %{...} are allowed.

Within the desired domain, the Alias_Schemes option is set to the Scheme name defined within the alias module.

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