[Sieve] Multiple email recipients, how?

[Stuart Henderson]

On 2019-11-22, Ralph Seichter via dovecot <dovecot at dovecot.org> wrote:
> * Robert via dovecot:
>
>> We use a simple system for routing emails to different email users by 
>> postfixing the addresses with the actual user: xxxJohn at domain; 
>> yyyJohn at domain etc all will be delivered to user John.
>> (This way John can invent a new email address on-the-fly and that will 
>> be delivered to his email box.)

But now you can't have a username like "BigJohn at domain". To avoid this
problem a separator character of some sort (that isn't used in a normal
email address at your site) is really wanted.

> This seems like a strange way achieve flexible email addresses. Are you
> aware of sub-addressing? It has been around for ages, and is supported
> by Dovecot (and Gmail, incidentally).
>
> Imagine an existing email account <alice at example.com>. If alice wants to
> use a subadress, she signs up with <alice+foo at example.com>, and Dovecot
> can automatically place incoming mail for that address into INBOX/foo
> (or just INBOX if INBOX/foo does not exist). Alice can use as many
> sub-adresses as she needs without anybody making config changes.

This method works well, but the separator character can be a problem.
"+" is traditional, but is widely blocked by website validators -
if you can use "-" or "." instead they're much more likely to be
accepted.