This is not true — the constraint is that the email must be delivered (not addressed) to one of these addresses to work. An example is the following setup which is what we and many of our customers use:
- (in Discourse) configure Postings category to accept inbound email sent to
postings@contoso.com - (on
contoso.commail server) configurepostings@contoso.comto forward to{ANYTHING}@contoso.discoursemail.com - end result: mail addressed to
postings@contoso.comgets sent to the Postings category
This functions effectively the same as:
- (in Discourse) configure Postings category to accept inbound email sent to
postings@contoso.discoursemail.com - end result: mail addressed to
postings@contoso.discoursemail.comgets sent to the Postings category