postfix-formula/postfix/files/mapping.j2

# Managed by config management
{#- Some files (mainly the aliases one) require key and values
    to be separated with a colon. For this `colon: True` should
    be passed to the template #}
{%- if colon is not defined %}
  {%- set colon = False %}
{%- endif %}
{%- macro format_value(key, value) %}
  {#- Some settings, like virtual_alias_maps can take multiple values. Handle this case. -#}
  {%- if value is iterable and value is not string -%}
{{ key }}{% if colon %}:{% endif %}	{{ value|join(", ") }}
  {%- else -%}
{{ key }}{% if colon %}:{% endif %}	{{ value }}
  {%- endif -%}
{%- endmacro %}

{%- if data is mapping %}
{% for key, value in data.items() %}
{{ format_value(key, value) }}
{%- endfor -%}
{%- else %}
{#- Some settings need order, handle OrderedDict #}
{% for item in data %}
{%-   set key, value = item.popitem() %}
{{ format_value(key, value) }}
{%- endfor -%}
{%- endif %}