Like Gmail, User able to append firstname.lastname@example.org to alias to their own gmail account. There are many benefits to use this email scheme and this is how to do.
This article based on DirectAdmin control panel and Exim.
In Exim, looking for the section
begin routers, for me I put in a section of
localuser and put following configuration
local_part_suffix = +* : -* : _* local_part_suffix_optional
This is allow user to add suffix as optional for something like email@example.com, firstname.lastname@example.org and email@example.com which will alias to firstname.lastname@example.org
When you put the configuration, check the log on
/var/log/exim/mainlog to see that there should not introduce new error when use user email alias.
After done, if you use the DirectAdmin, you may need to save to path
/usr/local/directadmin/templates/custom, so, in case that the exim got updated to the new version, it still be there.